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<button class="button is-small is-link">Go</button> </div> </div> </form> </div> </div> <nav class="pagination is-small is-centered breathe-horizontal" role="navigation" aria-label="pagination"> <a href="" class="pagination-previous is-invisible">Previous </a> <a href="/search/?searchtype=author&query=Barnes%2C+E&start=50" class="pagination-next" >Next </a> <ul class="pagination-list"> <li> <a href="/search/?searchtype=author&query=Barnes%2C+E&start=0" class="pagination-link is-current" aria-label="Goto page 1">1 </a> </li> <li> <a href="/search/?searchtype=author&query=Barnes%2C+E&start=50" class="pagination-link " aria-label="Page 2" aria-current="page">2 </a> </li> </ul> </nav> <ol class="breathe-horizontal" start="1"> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2408.00252">arXiv:2408.00252</a> <span> [<a href="https://arxiv.org/pdf/2408.00252">pdf</a>, <a href="https://arxiv.org/format/2408.00252">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Quantum thermalization and Floquet engineering in a spin ensemble with a clock transition </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Lei%2C+M">Mi Lei</a>, <a href="/search/quant-ph?searchtype=author&query=Fukumori%2C+R">Rikuto Fukumori</a>, <a href="/search/quant-ph?searchtype=author&query=Wu%2C+C">Chun-Ju Wu</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S">Sophia Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Choi%2C+J">Joonhee Choi</a>, <a href="/search/quant-ph?searchtype=author&query=Faraon%2C+A">Andrei Faraon</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2408.00252v1-abstract-short" style="display: inline;"> Studying and controlling quantum many-body interactions is fundamentally important for quantum science and related emerging technologies. Optically addressable solid-state spins offer a promising platform for exploring various quantum many-body phenomena due to their scalability to a large Hilbert space. However, it is often challenging to probe many-body dynamics in solid-state spin systems due t… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2408.00252v1-abstract-full').style.display = 'inline'; document.getElementById('2408.00252v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2408.00252v1-abstract-full" style="display: none;"> Studying and controlling quantum many-body interactions is fundamentally important for quantum science and related emerging technologies. Optically addressable solid-state spins offer a promising platform for exploring various quantum many-body phenomena due to their scalability to a large Hilbert space. However, it is often challenging to probe many-body dynamics in solid-state spin systems due to large on-site disorder and undesired coupling to the environment. Here, we investigate an optically addressable solid-state spin system comprising a strongly interacting ensemble of millions of ytterbium-171 ions in a crystal. Notably, this platform features a clock transition that gives rise to pure long-range spin-exchange interactions, termed the dipolar XY model. Leveraging this unique feature, we investigate quantum thermalization by varying the relative ratio of interaction strength to disorder, dynamically engineering the XY model into other many-body Hamiltonian models, and realizing a time-crystalline phase of matter through periodic driving. Our findings indicate that an ensemble of rare-earth ions serves as a versatile testbed for many-body physics and offers valuable insights for advancing quantum technologies. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2408.00252v1-abstract-full').style.display = 'none'; document.getElementById('2408.00252v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 31 July, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2024. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2407.15777">arXiv:2407.15777</a> <span> [<a href="https://arxiv.org/pdf/2407.15777">pdf</a>, <a href="https://arxiv.org/format/2407.15777">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Optimization complexity and resource minimization of emitter-based photonic graph state generation protocols </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Takou%2C+E">Evangelia Takou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2407.15777v1-abstract-short" style="display: inline;"> Photonic graph states are important for measurement- and fusion-based quantum computing, quantum networks, and sensing. They can in principle be generated deterministically by using emitters to create the requisite entanglement. Finding ways to minimize the number of entangling gates between emitters and understanding the overall optimization complexity of such protocols is crucial for practical i… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.15777v1-abstract-full').style.display = 'inline'; document.getElementById('2407.15777v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2407.15777v1-abstract-full" style="display: none;"> Photonic graph states are important for measurement- and fusion-based quantum computing, quantum networks, and sensing. They can in principle be generated deterministically by using emitters to create the requisite entanglement. Finding ways to minimize the number of entangling gates between emitters and understanding the overall optimization complexity of such protocols is crucial for practical implementations. Here, we address these issues using graph theory concepts. We develop optimizers that minimize the number of entangling gates, reducing them by up to 75$\%$ compared to naive schemes for moderately sized random graphs. While the complexity of optimizing emitter-emitter CNOT counts is likely NP-hard, we are able to develop heuristics based on strong connections between graph transformations and the optimization of stabilizer circuits. These patterns allow us to process large graphs and still achieve a reduction of up to $66\%$ in emitter CNOTs, without relying on subtle metrics such as edge density. We find the optimal emission orderings and circuits to prepare unencoded and encoded repeater graph states of any size, achieving global minimization of emitter and CNOT resources despite the average NP-hardness of both optimization problems. We further study the locally equivalent orbit of graphs. Although enumerating orbits is $\#$P complete for arbitrary graphs, we analytically calculate the size of the orbit of repeater graphs and find a procedure to generate the orbit for any repeater size. Finally, we inspect the entangling gate cost of preparing any graph from a given orbit and show that we can achieve the same optimal CNOT count across the orbit. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.15777v1-abstract-full').style.display = 'none'; document.getElementById('2407.15777v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 July, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">41 pages, 29 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2407.08696">arXiv:2407.08696</a> <span> [<a href="https://arxiv.org/pdf/2407.08696">pdf</a>, <a href="https://arxiv.org/format/2407.08696">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Reducing the Resources Required by ADAPT-VQE Using Coupled Exchange Operators and Improved Subroutines </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Ram%C3%B4a%2C+M">Mafalda Ram么a</a>, <a href="/search/quant-ph?searchtype=author&query=Anastasiou%2C+P+G">Panagiotis G. Anastasiou</a>, <a href="/search/quant-ph?searchtype=author&query=Santos%2C+L+P">Luis Paulo Santos</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2407.08696v1-abstract-short" style="display: inline;"> Adaptive variational quantum algorithms arguably offer the best prospects for quantum advantage in the NISQ era. Since the inception of the first such algorithm, ADAPT-VQE, many improvements have appeared in the literature. We combine the key improvements along with a novel operator pool -- which we term Coupled Exchange Operator (CEO) pool -- to assess the cost of running state-of-the-art ADAPT-V… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.08696v1-abstract-full').style.display = 'inline'; document.getElementById('2407.08696v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2407.08696v1-abstract-full" style="display: none;"> Adaptive variational quantum algorithms arguably offer the best prospects for quantum advantage in the NISQ era. Since the inception of the first such algorithm, ADAPT-VQE, many improvements have appeared in the literature. We combine the key improvements along with a novel operator pool -- which we term Coupled Exchange Operator (CEO) pool -- to assess the cost of running state-of-the-art ADAPT-VQE on hardware in terms of measurement counts and circuit depth. We show a dramatic reduction of these quantum resources compared to the early versions of the algorithm. We also find that our state-of-the-art CEO-ADAPT-VQE outperforms UCCSD, the most widely regarded static VQE ansatz, in all relevant metrics. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2407.08696v1-abstract-full').style.display = 'none'; document.getElementById('2407.08696v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 11 July, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2024. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2406.10913">arXiv:2406.10913</a> <span> [<a href="https://arxiv.org/pdf/2406.10913">pdf</a>, <a href="https://arxiv.org/format/2406.10913">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Minimal evolution times for fast, pulse-based state preparation in silicon spin qubits </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Long%2C+C+K">Christopher K. Long</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+C+H+W">Crispin H. W. Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Martins%2C+F">Frederico Martins</a>, <a href="/search/quant-ph?searchtype=author&query=Arvidsson-Shukur%2C+D+R+M">David R. M. Arvidsson-Shukur</a>, <a href="/search/quant-ph?searchtype=author&query=Mertig%2C+N">Normann Mertig</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2406.10913v1-abstract-short" style="display: inline;"> Standing as one of the most significant barriers to reaching quantum advantage, state-preparation fidelities on noisy intermediate-scale quantum processors suffer from quantum-gate errors, which accumulate over time. A potential remedy is pulse-based state preparation. We numerically investigate the minimal evolution times (METs) attainable by optimizing (microwave and exchange) pulses on silicon… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2406.10913v1-abstract-full').style.display = 'inline'; document.getElementById('2406.10913v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2406.10913v1-abstract-full" style="display: none;"> Standing as one of the most significant barriers to reaching quantum advantage, state-preparation fidelities on noisy intermediate-scale quantum processors suffer from quantum-gate errors, which accumulate over time. A potential remedy is pulse-based state preparation. We numerically investigate the minimal evolution times (METs) attainable by optimizing (microwave and exchange) pulses on silicon hardware. We investigate two state preparation tasks. First, we consider the preparation of molecular ground states and find the METs for H$_2$, HeH$^+$, and LiH to be 2.4 ns, 4.4 ns, and 27.2 ns, respectively. Second, we consider transitions between arbitrary states and find the METs for transitions between arbitrary four-qubit states to be below 50 ns. For comparison, connecting arbitrary two-qubit states via one- and two-qubit gates on the same silicon processor requires approximately 200 ns. This comparison indicates that pulse-based state preparation is likely to utilize the coherence times of silicon hardware more efficiently than gate-based state preparation. Finally, we quantify the effect of silicon device parameters on the MET. We show that increasing the maximal exchange amplitude from 10 MHz to 1 GHz accelerates the METs, e.g., for H$_2$ from 84.3 ns to 2.4 ns. This demonstrates the importance of fast exchange. We also show that increasing the maximal amplitude of the microwave drive from 884 kHz to 56.6 MHz shortens state transitions, e.g., for two-qubit states from 1000 ns to 25 ns. Our results bound both the state-preparation times for general quantum algorithms and the execution times of variational quantum algorithms with silicon spin qubits. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2406.10913v1-abstract-full').style.display = 'none'; document.getElementById('2406.10913v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 16 June, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 + (7) pages, 6 figs, comments are welcomed</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.15166">arXiv:2405.15166</a> <span> [<a href="https://arxiv.org/pdf/2405.15166">pdf</a>, <a href="https://arxiv.org/format/2405.15166">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Parameterization and optimizability of pulse-level VQEs </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Sherbert%2C+K+M">Kyle M Sherbert</a>, <a href="/search/quant-ph?searchtype=author&query=Amer%2C+H">Hisham Amer</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J Mayhall</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2405.15166v1-abstract-short" style="display: inline;"> In conventional variational quantum eigensolvers (VQEs), trial states are prepared by applying series of parameterized gates to a reference state, with the gate parameters being varied to minimize the energy of the target system. Recognizing that the gates are intermediates which are ultimately compiled into a set of control pulses to be applied to each qubit in the lab, the recently proposed ctrl… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.15166v1-abstract-full').style.display = 'inline'; document.getElementById('2405.15166v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.15166v1-abstract-full" style="display: none;"> In conventional variational quantum eigensolvers (VQEs), trial states are prepared by applying series of parameterized gates to a reference state, with the gate parameters being varied to minimize the energy of the target system. Recognizing that the gates are intermediates which are ultimately compiled into a set of control pulses to be applied to each qubit in the lab, the recently proposed ctrl-VQE algorithm takes the amplitudes, frequencies, and phases of the pulse as the variational parameters used to minimize the molecular energy. In this work, we explore how all three degrees of freedom interrelate with one another. To this end, we consider several distinct strategies to parameterize the control pulses, assessing each one through numerical simulations of a transmon-like device. For each parameterization, we contrast the pulse duration required to prepare a good ansatz, and the difficulty to optimize that ansatz from a well-defined initial state. We deduce several guiding heuristics to implement practical ctrl-VQE in hardware, which we anticipate will generalize for generic device architectures. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.15166v1-abstract-full').style.display = 'none'; document.getElementById('2405.15166v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages (10 of main text), 6 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.15148">arXiv:2405.15148</a> <span> [<a href="https://arxiv.org/pdf/2405.15148">pdf</a>, <a href="https://arxiv.org/ps/2405.15148">ps</a>, <a href="https://arxiv.org/format/2405.15148">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Dynamically corrected gates in silicon singlet-triplet spin qubits </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Walelign%2C+H+Y">Habitamu Y. Walelign</a>, <a href="/search/quant-ph?searchtype=author&query=Cai%2C+X">Xinxin Cai</a>, <a href="/search/quant-ph?searchtype=author&query=Li%2C+B">Bikun Li</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Nichol%2C+J+M">John M. Nichol</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2405.15148v2-abstract-short" style="display: inline;"> Fault-tolerant quantum computation requires low physical-qubit gate errors. Many approaches exist to reduce gate errors, including both hardware- and control-optimization strategies. Dynamically corrected gates are designed to cancel specific errors and offer the potential for high-fidelity gates, but they have yet to be implemented in singlet-triplet spin qubits in semiconductor quantum dots, due… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.15148v2-abstract-full').style.display = 'inline'; document.getElementById('2405.15148v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.15148v2-abstract-full" style="display: none;"> Fault-tolerant quantum computation requires low physical-qubit gate errors. Many approaches exist to reduce gate errors, including both hardware- and control-optimization strategies. Dynamically corrected gates are designed to cancel specific errors and offer the potential for high-fidelity gates, but they have yet to be implemented in singlet-triplet spin qubits in semiconductor quantum dots, due in part to the stringent control constraints in these systems. In this work, we experimentally implement dynamically corrected gates designed to mitigate hyperfine noise in a singlet-triplet qubit realized in a Si/SiGe double quantum dot. The corrected gates reduce infidelities by about a factor of three, resulting in gate fidelities above 0.99 for both identity and Hadamard gates. The gate performances depend sensitively on pulse distortions, and their specific performance reveals an unexpected distortion in our experimental setup. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.15148v2-abstract-full').style.display = 'none'; document.getElementById('2405.15148v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 11 July, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 23 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages including supplementary materials. 10 figures including those in the supplementary material</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.14027">arXiv:2405.14027</a> <span> [<a href="https://arxiv.org/pdf/2405.14027">pdf</a>, <a href="https://arxiv.org/format/2405.14027">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Mesoscale and Nanoscale Physics">cond-mat.mes-hall</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Ballast charges for semiconductor spin qubits </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Choi%2C+Y">Yujun Choi</a>, <a href="/search/quant-ph?searchtype=author&query=Nichol%2C+J+M">John M. Nichol</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2405.14027v1-abstract-short" style="display: inline;"> Semiconductor spin qubits are an attractive platform for quantum computing, but their performance is degraded primarily by fluctuating electromagnetic environments. We introduce the concept of ballast charges, which are induced charges on the surface of an additional screening layer situated below the qubits. The counteractive behavior of these charges can significantly reduce the power spectral d… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.14027v1-abstract-full').style.display = 'inline'; document.getElementById('2405.14027v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.14027v1-abstract-full" style="display: none;"> Semiconductor spin qubits are an attractive platform for quantum computing, but their performance is degraded primarily by fluctuating electromagnetic environments. We introduce the concept of ballast charges, which are induced charges on the surface of an additional screening layer situated below the qubits. The counteractive behavior of these charges can significantly reduce the power spectral density associated with fluctuations from two-level systems that contribute to charge noise. Our simulations show that the dephasing time of a spin qubit in a Si/SiGe device increases by a factor of 4 to 6 on average when using this method. We also discuss the physical implementation and potential challenges of this approach. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.14027v1-abstract-full').style.display = 'none'; document.getElementById('2405.14027v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, 3 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2405.10778">arXiv:2405.10778</a> <span> [<a href="https://arxiv.org/pdf/2405.10778">pdf</a>, <a href="https://arxiv.org/format/2405.10778">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> High-throughput assessment of defect-nuclear spin register controllability for quantum memory applications </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Dakis%2C+F">Filippos Dakis</a>, <a href="/search/quant-ph?searchtype=author&query=Takou%2C+E">Evangelia Takou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2405.10778v2-abstract-short" style="display: inline;"> Quantum memories play a key role in facilitating tasks within quantum networks and quantum information processing, including secure communications, advanced quantum sensing, and distributed quantum computing. Progress in characterizing large nuclear spin registers coupled to defect electronic spins has been significant, but selecting memory qubits remains challenging due to the multitude of possib… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.10778v2-abstract-full').style.display = 'inline'; document.getElementById('2405.10778v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2405.10778v2-abstract-full" style="display: none;"> Quantum memories play a key role in facilitating tasks within quantum networks and quantum information processing, including secure communications, advanced quantum sensing, and distributed quantum computing. Progress in characterizing large nuclear spin registers coupled to defect electronic spins has been significant, but selecting memory qubits remains challenging due to the multitude of possible assignments. Numerical simulations for evaluating entangling gate fidelities encounter obstacles, restricting research to small registers, while experimental investigations are time-consuming and often limited to well-understood samples. Here we present an efficient methodology for systematically assessing the controllability of defect systems coupled to nuclear spin registers. We showcase the approach by investigating the generation of entanglement links between defects in SiC and randomly selected sets of nuclear spins within the two-species ($^{13}$C and $^{29}$Si) nuclear register. We quantify the performance of entangling gate operations and present the achievable gate fidelities, considering both the size of the register and the presence of unwanted nuclear spins. We find that some control sequences perform better than others depending on the number of target versus bath nuclei. This efficient approach is a guide for both experimental investigation and engineering, facilitating the high-throughput exploration of suitable defect systems for quantum memories. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2405.10778v2-abstract-full').style.display = 'none'; document.getElementById('2405.10778v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 21 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 17 May, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 7 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2402.18001">arXiv:2402.18001</a> <span> [<a href="https://arxiv.org/pdf/2402.18001">pdf</a>, <a href="https://arxiv.org/format/2402.18001">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Mesoscale and Nanoscale Physics">cond-mat.mes-hall</span> </div> </div> <p class="title is-5 mathjax"> Hilbert Space Fragmentation and Subspace Scar Time-Crystallinity in Driven Homogeneous Central-Spin Models </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Kumar%2C+A">Abhishek Kumar</a>, <a href="/search/quant-ph?searchtype=author&query=Frantzeskakis%2C+R">Rafail Frantzeskakis</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2402.18001v1-abstract-short" style="display: inline;"> We study the stroboscopic non-equilibrium quantum dynamics of periodically kicked Hamiltonians involving homogeneous central-spin interactions. The system exhibits a strong fragmentation of Hilbert space into four-dimensional Floquet-Krylov subspaces, which oscillate between two disjointed two-dimensional subspaces and thus break the discrete time-translation symmetry of the system. Our analytical… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2402.18001v1-abstract-full').style.display = 'inline'; document.getElementById('2402.18001v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2402.18001v1-abstract-full" style="display: none;"> We study the stroboscopic non-equilibrium quantum dynamics of periodically kicked Hamiltonians involving homogeneous central-spin interactions. The system exhibits a strong fragmentation of Hilbert space into four-dimensional Floquet-Krylov subspaces, which oscillate between two disjointed two-dimensional subspaces and thus break the discrete time-translation symmetry of the system. Our analytical and numerical analyses reveal that fully polarized states of the satellite spins exhibit fragmentations that are stable against perturbations and have high overlap with Floquet eigenstates of atypically low bipartite entanglement entropy (scar states). We present evidence of robust time-crystalline behavior in the form of a period doubling of the total magnetization of fully polarized satellite spin states that persists over long time scales. We compute non-equilibrium phase diagrams with respect to a magnetic field, coupling terms, and pulse error for various interaction types, including Heisenberg, Ising, XXZ, and XX. We also discuss possible experimental realizations of scar time crystals in color center, quantum dot, and rare-earth ion platforms. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2402.18001v1-abstract-full').style.display = 'none'; document.getElementById('2402.18001v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 27 February, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17 pages, 9 figures, 1 table</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2401.05172">arXiv:2401.05172</a> <span> [<a href="https://arxiv.org/pdf/2401.05172">pdf</a>, <a href="https://arxiv.org/format/2401.05172">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/2058-9565/ad904e">10.1088/2058-9565/ad904e <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Reducing measurement costs by recycling the Hessian in adaptive variational quantum algorithms </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Ram%C3%B4a%2C+M">Mafalda Ram么a</a>, <a href="/search/quant-ph?searchtype=author&query=Santos%2C+L+P">Luis Paulo Santos</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2401.05172v2-abstract-short" style="display: inline;"> Adaptive protocols enable the construction of more efficient state preparation circuits in variational quantum algorithms (VQAs) by utilizing data obtained from the quantum processor during the execution of the algorithm. This idea originated with ADAPT-VQE, an algorithm that iteratively grows the state preparation circuit operator by operator, with each new operator accompanied by a new variation… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2401.05172v2-abstract-full').style.display = 'inline'; document.getElementById('2401.05172v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2401.05172v2-abstract-full" style="display: none;"> Adaptive protocols enable the construction of more efficient state preparation circuits in variational quantum algorithms (VQAs) by utilizing data obtained from the quantum processor during the execution of the algorithm. This idea originated with ADAPT-VQE, an algorithm that iteratively grows the state preparation circuit operator by operator, with each new operator accompanied by a new variational parameter, and where all parameters acquired thus far are optimized in each iteration. In ADAPT-VQE and other adaptive VQAs that followed it, it has been shown that initializing parameters to their optimal values from the previous iteration speeds up convergence and avoids shallow local traps in the parameter landscape. However, no other data from the optimization performed at one iteration is carried over to the next. In this work, we propose an improved quasi-Newton optimization protocol specifically tailored to adaptive VQAs. The distinctive feature in our proposal is that approximate second derivatives of the cost function are recycled across iterations in addition to parameter values. We implement a quasi-Newton optimizer where an approximation to the inverse Hessian matrix is continuously built and grown across the iterations of an adaptive VQA. The resulting algorithm has the flavor of a continuous optimization where the dimension of the search space is augmented when the gradient norm falls below a given threshold. We show that this inter-optimization exchange of second-order information leads the Hessian in the state of the optimizer to better approximate the exact Hessian. As a result, our method achieves a superlinear convergence rate even in situations where the typical quasi-Newton optimizer converges only linearly. Our protocol decreases the measurement costs in implementing adaptive VQAs on quantum hardware as well as the runtime of their classical simulation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2401.05172v2-abstract-full').style.display = 'none'; document.getElementById('2401.05172v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 18 November, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 10 January, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Quantum Sci. Technol. 10 (2024) 015031 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2310.09694">arXiv:2310.09694</a> <span> [<a href="https://arxiv.org/pdf/2310.09694">pdf</a>, <a href="https://arxiv.org/format/2310.09694">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> ADAPT-QAOA with a classically inspired initial state </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Sridhar%2C+V+K">Vishvesha K. Sridhar</a>, <a href="/search/quant-ph?searchtype=author&query=Chen%2C+Y">Yanzhu Chen</a>, <a href="/search/quant-ph?searchtype=author&query=Gard%2C+B">Bryan Gard</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2310.09694v1-abstract-short" style="display: inline;"> Quantum computing may provide advantage in solving classical optimization problems. One promising algorithm is the quantum approximate optimization algorithm (QAOA). There have been many proposals for improving this algorithm, such as using an initial state informed by classical approximation solutions. A variation of QAOA called ADAPT-QAOA constructs the ansatz dynamically and can speed up conver… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2310.09694v1-abstract-full').style.display = 'inline'; document.getElementById('2310.09694v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2310.09694v1-abstract-full" style="display: none;"> Quantum computing may provide advantage in solving classical optimization problems. One promising algorithm is the quantum approximate optimization algorithm (QAOA). There have been many proposals for improving this algorithm, such as using an initial state informed by classical approximation solutions. A variation of QAOA called ADAPT-QAOA constructs the ansatz dynamically and can speed up convergence. However, it faces the challenge of frequently converging to excited states which correspond to local minima in the energy landscape, limiting its performance. In this work, we propose to start ADAPT-QAOA with an initial state inspired by a classical approximation algorithm. Through numerical simulations we show that this new algorithm can reach the same accuracy with fewer layers than the standard QAOA and the original ADAPT-QAOA. It also appears to be less prone to the problem of converging to excited states. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2310.09694v1-abstract-full').style.display = 'none'; document.getElementById('2310.09694v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 14 October, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, 8 figures. Comments are welcome</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2308.09035">arXiv:2308.09035</a> <span> [<a href="https://arxiv.org/pdf/2308.09035">pdf</a>, <a href="https://arxiv.org/format/2308.09035">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Protocol for nearly deterministic parity projection on two photonic qubits </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Liu%2C+C">Chenxu Liu</a>, <a href="/search/quant-ph?searchtype=author&query=Frantzeskakis%2C+R">Rafail Frantzeskakis</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2308.09035v2-abstract-short" style="display: inline;"> Photonic parity projection plays a significant role in photonic quantum information processing. Non-destructive parity projections normally require high-fidelity Controlled-Z gates between photonic and matter qubits, which can be experimentally demanding. In this paper, we propose a nearly deterministic parity projection protocol on two photonic qubits which only requires stable matter-photon Cont… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.09035v2-abstract-full').style.display = 'inline'; document.getElementById('2308.09035v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2308.09035v2-abstract-full" style="display: none;"> Photonic parity projection plays a significant role in photonic quantum information processing. Non-destructive parity projections normally require high-fidelity Controlled-Z gates between photonic and matter qubits, which can be experimentally demanding. In this paper, we propose a nearly deterministic parity projection protocol on two photonic qubits which only requires stable matter-photon Controlled-Phase gates. The fact that our protocol does not require perfect Controlled-Z gates makes it more amenable to experimental implementation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2308.09035v2-abstract-full').style.display = 'none'; document.getElementById('2308.09035v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 26 September, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 17 August, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12+6 pages, 11 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2307.13523">arXiv:2307.13523</a> <span> [<a href="https://arxiv.org/pdf/2307.13523">pdf</a>, <a href="https://arxiv.org/format/2307.13523">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Long-distance photon-mediated and short-distance entangling gates in three-qubit quantum dot spin systems </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Estakhri%2C+N+M">Nooshin M. Estakhri</a>, <a href="/search/quant-ph?searchtype=author&query=Warren%2C+A">Ada Warren</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2307.13523v1-abstract-short" style="display: inline;"> Superconducting microwave resonator couplers will likely become an essential component in modular semiconductor quantum dot (QD) spin qubit processors, as they help alleviate cross-talk and wiring issues as the number of qubits increases. Here, we focus on a three-qubit system composed of two modules: a two-electron triple QD resonator-coupled to a single-electron double QD. Using a combination of… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2307.13523v1-abstract-full').style.display = 'inline'; document.getElementById('2307.13523v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2307.13523v1-abstract-full" style="display: none;"> Superconducting microwave resonator couplers will likely become an essential component in modular semiconductor quantum dot (QD) spin qubit processors, as they help alleviate cross-talk and wiring issues as the number of qubits increases. Here, we focus on a three-qubit system composed of two modules: a two-electron triple QD resonator-coupled to a single-electron double QD. Using a combination of analytical techniques and numerical results, we derive an effective Hamiltonian that describes the three-qubit logical subspace and show that it accurately captures the dynamics of the system. We examine the performance of short-range and long-range entangling gates, revealing the effect of a spectator qubit in reducing the gate fidelities in both cases. We further study the competition between non-adiabatic errors and spectator-associated errors in short-range operations and quantify their relative importance across practical parameter ranges for short and long gate times. We also analyze the impact of charge noise together with residual coupling to the spectator qubit on inter-module entangling gates and find that for current experimental settings, leakage errors are the main source of infidelities in these operations. Our results help pave the way toward identifying optimal modular QD architectures for quantum information processing on semiconductor chips. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2307.13523v1-abstract-full').style.display = 'none'; document.getElementById('2307.13523v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 25 July, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 5 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2306.03227">arXiv:2306.03227</a> <span> [<a href="https://arxiv.org/pdf/2306.03227">pdf</a>, <a href="https://arxiv.org/format/2306.03227">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> How to really measure operator gradients in ADAPT-VQE </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Anastasiou%2C+P+G">Panagiotis G. Anastasiou</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2306.03227v2-abstract-short" style="display: inline;"> ADAPT-VQE is one of the leading VQE algorithms which circumvents the choice-of-ansatz conundrum by iteratively growing compact and arbitrarily accurate problem-tailored ans盲tze. However, for hardware-efficient operator pools, the gradient-measurement step of the algorithm requires the estimation of $O(N^8)$ observables, which may represent a bottleneck for relevant system sizes on real devices. We… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.03227v2-abstract-full').style.display = 'inline'; document.getElementById('2306.03227v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2306.03227v2-abstract-full" style="display: none;"> ADAPT-VQE is one of the leading VQE algorithms which circumvents the choice-of-ansatz conundrum by iteratively growing compact and arbitrarily accurate problem-tailored ans盲tze. However, for hardware-efficient operator pools, the gradient-measurement step of the algorithm requires the estimation of $O(N^8)$ observables, which may represent a bottleneck for relevant system sizes on real devices. We present an efficient strategy for measuring the pool gradients based on simultaneously measuring commuting observables. We argue that our approach is relatively robust to shot-noise effects, and show that measuring the pool gradients is in fact only $O(N)$ times as expensive as a naive VQE iteration. Our proposed measurement strategy significantly ameliorates the measurement overhead of ADAPT-VQE and brings us one step closer to practical implementations on real devices. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.03227v2-abstract-full').style.display = 'none'; document.getElementById('2306.03227v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 29 September, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 5 June, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, 2 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2303.00893">arXiv:2303.00893</a> <span> [<a href="https://arxiv.org/pdf/2303.00893">pdf</a>, <a href="https://arxiv.org/format/2303.00893">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Mesoscale and Nanoscale Physics">cond-mat.mes-hall</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevB.108.075302">10.1103/PhysRevB.108.075302 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Time-crystalline behavior in central-spin models with Heisenberg interactions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Frantzeskakis%2C+R">Rafail Frantzeskakis</a>, <a href="/search/quant-ph?searchtype=author&query=Van+Dyke%2C+J">John Van Dyke</a>, <a href="/search/quant-ph?searchtype=author&query=Zaporski%2C+L">Leon Zaporski</a>, <a href="/search/quant-ph?searchtype=author&query=Gangloff%2C+D+A">Dorian A. Gangloff</a>, <a href="/search/quant-ph?searchtype=author&query=Gall%2C+C+L">Claire Le Gall</a>, <a href="/search/quant-ph?searchtype=author&query=Atat%C3%BCre%2C+M">Mete Atat眉re</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2303.00893v2-abstract-short" style="display: inline;"> Time-crystalline behavior has been predicted and observed in quantum central-spin systems with periodic driving and Ising interactions. Here, we theoretically show that it can also arise in central-spin systems with Heisenberg interactions. We present two methods to achieve this: application of a sufficiently large Zeeman splitting on the central spin compared to the satellite spins, or else by ap… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2303.00893v2-abstract-full').style.display = 'inline'; document.getElementById('2303.00893v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2303.00893v2-abstract-full" style="display: none;"> Time-crystalline behavior has been predicted and observed in quantum central-spin systems with periodic driving and Ising interactions. Here, we theoretically show that it can also arise in central-spin systems with Heisenberg interactions. We present two methods to achieve this: application of a sufficiently large Zeeman splitting on the central spin compared to the satellite spins, or else by applying additional pulses to the central spin every Floquet period. In both cases, we show that the system exhibits a subharmonic response in spin magnetizations in the presence of disorder for both pure Heisenberg and XXZ interactions. Our results pertain to any XXZ central-spin system, including hyperfine-coupled electron-nuclear systems in quantum dots or color centers. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2303.00893v2-abstract-full').style.display = 'none'; document.getElementById('2303.00893v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 11 October, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 1 March, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">20 pages, 18 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. B 108, 075302 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2302.07908">arXiv:2302.07908</a> <span> [<a href="https://arxiv.org/pdf/2302.07908">pdf</a>, <a href="https://arxiv.org/format/2302.07908">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Linear optical logical Bell state measurements with optimal loss-tolerance threshold </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Hilaire%2C+P">Paul Hilaire</a>, <a href="/search/quant-ph?searchtype=author&query=Castor%2C+Y">Yaron Castor</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Grosshans%2C+F">Fr茅d茅ric Grosshans</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2302.07908v2-abstract-short" style="display: inline;"> Quantum threshold theorems impose hard limits on the hardware capabilities to process quantum information. We derive tight and fundamental upper bounds to loss-tolerance thresholds in different linear-optical quantum information processing settings through an adversarial framework, taking into account the intrinsically probabilistic nature of linear optical Bell measurements. For logical Bell stat… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2302.07908v2-abstract-full').style.display = 'inline'; document.getElementById('2302.07908v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2302.07908v2-abstract-full" style="display: none;"> Quantum threshold theorems impose hard limits on the hardware capabilities to process quantum information. We derive tight and fundamental upper bounds to loss-tolerance thresholds in different linear-optical quantum information processing settings through an adversarial framework, taking into account the intrinsically probabilistic nature of linear optical Bell measurements. For logical Bell state measurements - ubiquitous operations in photonic quantum information - we demonstrate analytically that linear optics can achieve the fundamental loss threshold imposed by the no-cloning theorem even though, following the work of Lee et al., (Phys. Rev. A 100, 052303 (2019)), the constraint was widely assumed to be stricter. We spotlight the assumptions of the latter publication and find their bound holds for a logical Bell measurement built from adaptive physical linear-optical Bell measurements. We also give an explicit even stricter bound for non-adaptive Bell measurements. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2302.07908v2-abstract-full').style.display = 'none'; document.getElementById('2302.07908v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 May, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 15 February, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17pages, 14 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2302.05580">arXiv:2302.05580</a> <span> [<a href="https://arxiv.org/pdf/2302.05580">pdf</a>, <a href="https://arxiv.org/format/2302.05580">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.22331/q-2024-03-28-1304">10.22331/q-2024-03-28-1304 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Generation of genuine all-way entanglement in defect-nuclear spin systems through dynamical decoupling sequences </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Takou%2C+E">Evangelia Takou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2302.05580v3-abstract-short" style="display: inline;"> Multipartite entangled states are an essential resource for sensing, quantum error correction, and cryptography. Color centers in solids are one of the leading platforms for quantum networking due to the availability of a nuclear spin memory that can be entangled with the optically active electronic spin through dynamical decoupling sequences. Creating electron-nuclear entangled states in these sy… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2302.05580v3-abstract-full').style.display = 'inline'; document.getElementById('2302.05580v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2302.05580v3-abstract-full" style="display: none;"> Multipartite entangled states are an essential resource for sensing, quantum error correction, and cryptography. Color centers in solids are one of the leading platforms for quantum networking due to the availability of a nuclear spin memory that can be entangled with the optically active electronic spin through dynamical decoupling sequences. Creating electron-nuclear entangled states in these systems is a difficult task as the always-on hyperfine interactions prohibit complete isolation of the target dynamics from the unwanted spin bath. While this emergent cross-talk can be alleviated by prolonging the entanglement generation, the gate durations quickly exceed coherence times. Here we show how to prepare high-quality GHZ$_M$-like states with minimal cross-talk. We introduce the $M$-tangling power of an evolution operator, which allows us to verify genuine all-way correlations. Using experimentally measured hyperfine parameters of an NV center spin in diamond coupled to carbon-13 lattice spins, we show how to use sequential or single-shot entangling operations to prepare GHZ$_M$-like states of up to $M=10$ qubits within time constraints that saturate bounds on $M$-way correlations. We study the entanglement of mixed electron-nuclear states and develop a non-unitary $M$-tangling power which additionally captures correlations arising from all unwanted nuclear spins. We further derive a non-unitary $M$-tangling power which incorporates the impact of electronic dephasing errors on the $M$-way correlations. Finally, we inspect the performance of our protocols in the presence of experimentally reported pulse errors, finding that XY decoupling sequences can lead to high-fidelity GHZ state preparation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2302.05580v3-abstract-full').style.display = 'none'; document.getElementById('2302.05580v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 March, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 10 February, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">43 pages, 18 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Quantum 8, 1304 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2211.13248">arXiv:2211.13248</a> <span> [<a href="https://arxiv.org/pdf/2211.13248">pdf</a>, <a href="https://arxiv.org/format/2211.13248">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevA.108.012407">10.1103/PhysRevA.108.012407 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Designing dynamically corrected gates robust to multiple noise sources using geometric space curves </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Nelson%2C+H+T">Hunter T. Nelson</a>, <a href="/search/quant-ph?searchtype=author&query=Piliouras%2C+E">Evangelos Piliouras</a>, <a href="/search/quant-ph?searchtype=author&query=Connelly%2C+K">Kyle Connelly</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2211.13248v1-abstract-short" style="display: inline;"> Noise-induced gate errors remain one of the main obstacles to realizing a broad range of quantum information technologies. Dynamical error suppression using carefully designed control schemes is critical for overcoming this challenge. Such schemes must be able to correct against multiple noise sources simultaneously afflicting a qubit in order to reach error correction thresholds. Here, we present… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2211.13248v1-abstract-full').style.display = 'inline'; document.getElementById('2211.13248v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2211.13248v1-abstract-full" style="display: none;"> Noise-induced gate errors remain one of the main obstacles to realizing a broad range of quantum information technologies. Dynamical error suppression using carefully designed control schemes is critical for overcoming this challenge. Such schemes must be able to correct against multiple noise sources simultaneously afflicting a qubit in order to reach error correction thresholds. Here, we present a general framework for designing control fields that simultaneous suppress both noise in the fields themselves as well as transverse dephasing noise. Using the recently developed Space Curve Quantum Control formalism, in which robust quantum evolution is mapped to closed geometric curves in a multidimensional Euclidean space, we derive necessary and sufficient conditions that guarantee the cancellation of both types of noise to leading order. We present several techniques for solving these conditions and provide explicit examples of error-resistant control fields. Our work also sheds light on the relation between holonomic evolution and the suppression of control field errors. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2211.13248v1-abstract-full').style.display = 'none'; document.getElementById('2211.13248v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 November, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 4 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2211.13242">arXiv:2211.13242</a> <span> [<a href="https://arxiv.org/pdf/2211.13242">pdf</a>, <a href="https://arxiv.org/format/2211.13242">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PRXQuantum.5.020346">10.1103/PRXQuantum.5.020346 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Deterministic generation of qudit photonic graph states from quantum emitters </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Raissi%2C+Z">Zahra Raissi</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2211.13242v2-abstract-short" style="display: inline;"> We propose and analyze deterministic protocols to generate qudit photonic graph states from quantum emitters. We show that our approach can be applied to generate any qudit graph state, and we exemplify it by constructing protocols to generate one- and two-dimensional qudit cluster states, absolutely maximally entangled states, and logical states of quantum error correcting codes. Some of these pr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2211.13242v2-abstract-full').style.display = 'inline'; document.getElementById('2211.13242v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2211.13242v2-abstract-full" style="display: none;"> We propose and analyze deterministic protocols to generate qudit photonic graph states from quantum emitters. We show that our approach can be applied to generate any qudit graph state, and we exemplify it by constructing protocols to generate one- and two-dimensional qudit cluster states, absolutely maximally entangled states, and logical states of quantum error correcting codes. Some of these protocols make use of time-delayed feedback, while others do not. The only additional resource requirement compared to the qubit case is the ability to control multi-level emitters. These results significantly broaden the range of multi-photon entangled states that can be produced deterministically from quantum emitters. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2211.13242v2-abstract-full').style.display = 'none'; document.getElementById('2211.13242v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 29 February, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 23 November, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages, 10 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> PRX Quantum 5, 020346 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2210.02868">arXiv:2210.02868</a> <span> [<a href="https://arxiv.org/pdf/2210.02868">pdf</a>, <a href="https://arxiv.org/format/2210.02868">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Physics Education">physics.ed-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Popular Physics">physics.pop-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Hello Quantum World! A rigorous but accessible first-year university course in quantum information science </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2210.02868v2-abstract-short" style="display: inline;"> Addressing workforce shortages within the Quantum Information Science and Engineering (QISE) community requires attracting and retaining students from diverse backgrounds early on in their undergraduate education. Here, we describe a course we developed called Hello Quantum World! that introduces a broad range of fundamental quantum information and computation concepts in a rigorous way but withou… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2210.02868v2-abstract-full').style.display = 'inline'; document.getElementById('2210.02868v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2210.02868v2-abstract-full" style="display: none;"> Addressing workforce shortages within the Quantum Information Science and Engineering (QISE) community requires attracting and retaining students from diverse backgrounds early on in their undergraduate education. Here, we describe a course we developed called Hello Quantum World! that introduces a broad range of fundamental quantum information and computation concepts in a rigorous way but without requiring any knowledge of mathematics beyond high-school algebra nor any prior knowledge of quantum mechanics. Some of the topics covered include superposition, entanglement, quantum gates, teleportation, quantum algorithms, and quantum error correction. The course is designed for first-year undergraduate students, both those pursuing a degree in QISE and those who are seeking to be `quantum-aware'. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2210.02868v2-abstract-full').style.display = 'none'; document.getElementById('2210.02868v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 6 November, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 25 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">7 pages, 8 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2209.11430">arXiv:2209.11430</a> <span> [<a href="https://arxiv.org/pdf/2209.11430">pdf</a>, <a href="https://arxiv.org/format/2209.11430">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.22331/q-2023-02-16-924">10.22331/q-2023-02-16-924 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Performance analysis of quantum repeaters enabled by deterministically generated photonic graph states </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Zhan%2C+Y">Yuan Zhan</a>, <a href="/search/quant-ph?searchtype=author&query=Hilaire%2C+P">Paul Hilaire</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Sun%2C+S">Shuo Sun</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2209.11430v2-abstract-short" style="display: inline;"> By encoding logical qubits into specific types of photonic graph states, one can realize quantum repeaters that enable fast entanglement distribution rates approaching classical communication. However, the generation of these photonic graph states requires a formidable resource overhead using traditional approaches based on linear optics. Overcoming this challenge, a number of new schemes have bee… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.11430v2-abstract-full').style.display = 'inline'; document.getElementById('2209.11430v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2209.11430v2-abstract-full" style="display: none;"> By encoding logical qubits into specific types of photonic graph states, one can realize quantum repeaters that enable fast entanglement distribution rates approaching classical communication. However, the generation of these photonic graph states requires a formidable resource overhead using traditional approaches based on linear optics. Overcoming this challenge, a number of new schemes have been proposed that employ quantum emitters to deterministically generate photonic graph states. Although these schemes have the potential to significantly reduce the resource cost, a systematic comparison of the repeater performance among different encodings and different generation schemes is lacking. Here, we quantitatively analyze the performance of quantum repeaters based on two different graph states, i.e. the tree graph states and the repeater graph states. For both states, we compare the performance between two generation schemes, one based on a single quantum emitter coupled to ancillary matter qubits, and one based on a single quantum emitter coupled to a delayed feedback. We identify the numerically optimal scheme at different system parameters. Our analysis provides a clear guideline on the selection of the generation scheme for graph-state-based quantum repeaters, and lays out the parameter requirements for future experimental realizations of different schemes. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.11430v2-abstract-full').style.display = 'none'; document.getElementById('2209.11430v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 8 February, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 23 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 8 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Quantum 7, 924 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2209.10562">arXiv:2209.10562</a> <span> [<a href="https://arxiv.org/pdf/2209.10562">pdf</a>, <a href="https://arxiv.org/format/2209.10562">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevResearch.6.013254">10.1103/PhysRevResearch.6.013254 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> TETRIS-ADAPT-VQE: An adaptive algorithm that yields shallower, denser circuit ans盲tze </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Anastasiou%2C+P+G">Panagiotis G. Anastasiou</a>, <a href="/search/quant-ph?searchtype=author&query=Chen%2C+Y">Yanzhu Chen</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2209.10562v1-abstract-short" style="display: inline;"> Adaptive quantum variational algorithms are particularly promising for simulating strongly correlated systems on near-term quantum hardware, but they are not yet viable due, in large part, to the severe coherence time limitations on current devices. In this work, we introduce an algorithm called TETRIS-ADAPT-VQE, which iteratively builds up variational ans盲tze a few operators at a time in a way di… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.10562v1-abstract-full').style.display = 'inline'; document.getElementById('2209.10562v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2209.10562v1-abstract-full" style="display: none;"> Adaptive quantum variational algorithms are particularly promising for simulating strongly correlated systems on near-term quantum hardware, but they are not yet viable due, in large part, to the severe coherence time limitations on current devices. In this work, we introduce an algorithm called TETRIS-ADAPT-VQE, which iteratively builds up variational ans盲tze a few operators at a time in a way dictated by the problem being simulated. This algorithm is a modified version of the ADAPT-VQE algorithm in which the one-operator-at-a-time rule is lifted to allow for the addition of multiple operators with disjoint supports in each iteration. TETRIS-ADAPT-VQE results in denser but significantly shallower circuits, without increasing the number of CNOT gates or variational parameters. Its advantage over the original algorithm in terms of circuit depths increases with the system size. Moreover, the expensive step of measuring the energy gradient with respect to each candidate unitary at each iteration is performed only a fraction of the time compared to ADAPT-VQE. These improvements bring us closer to the goal of demonstrating a practical quantum advantage on quantum hardware. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.10562v1-abstract-full').style.display = 'none'; document.getElementById('2209.10562v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 21 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, 7 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2207.03063">arXiv:2207.03063</a> <span> [<a href="https://arxiv.org/pdf/2207.03063">pdf</a>, <a href="https://arxiv.org/ps/2207.03063">ps</a>, <a href="https://arxiv.org/format/2207.03063">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Symmetry breaking slows convergence of the ADAPT Variational Quantum Eigensolver </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Bertels%2C+L+W">Luke W. Bertels</a>, <a href="/search/quant-ph?searchtype=author&query=Grimsley%2C+H+R">Harper R. Grimsley</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2207.03063v1-abstract-short" style="display: inline;"> Because quantum simulation of molecular systems is expected to provide the strongest advantage over classical computing methods for systems exhibiting strong electron correlation, it is critical that the performance of VQEs be assessed for strongly correlated systems. For classical simulation, strong correlation often results in symmetry-breaking of the Hartree-Fock reference, leading to L枚wdin's… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2207.03063v1-abstract-full').style.display = 'inline'; document.getElementById('2207.03063v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2207.03063v1-abstract-full" style="display: none;"> Because quantum simulation of molecular systems is expected to provide the strongest advantage over classical computing methods for systems exhibiting strong electron correlation, it is critical that the performance of VQEs be assessed for strongly correlated systems. For classical simulation, strong correlation often results in symmetry-breaking of the Hartree-Fock reference, leading to L枚wdin's well-known ``symmetry dilemma'' whereby accuracy in the energy can be increased by breaking spin or spatial symmetries. Here, we explore the impact of symmetry breaking on the performance of ADAPT-VQE using two strongly correlated systems: (i) the ``fermionized" anisotropic Heisenberg model, where the anisotropy parameter controls the correlation in the system, and (ii) symmetrically-stretched linear \ce{H4}, where correlation increases with increasing H-H separation. In both of these cases, increasing the level of correlation of the system leads to spontaneous symmetry breaking (parity and $\hat{S}^{2}$, respectively) of the mean-field solutions. We analyze the role that symmetry breaking in the reference states and orbital mappings of the fermionic Hamiltonians have on the compactness and performance of ADAPT-VQE. We observe that improving the energy of the reference states by breaking symmetry has a deleterious effect on ADAPT-VQE by increasing the length of the ansatz necessary for energy convergence and exacerbating the problem of ``gradient troughs". <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2207.03063v1-abstract-full').style.display = 'none'; document.getElementById('2207.03063v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 6 July, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">16 pages, 5 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2206.14215">arXiv:2206.14215</a> <span> [<a href="https://arxiv.org/pdf/2206.14215">pdf</a>, <a href="https://arxiv.org/format/2206.14215">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Strongly Correlated Electrons">cond-mat.str-el</span> </div> </div> <p class="title is-5 mathjax"> Scaling adaptive quantum simulation algorithms via operator pool tiling </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Van+Dyke%2C+J+S">John S. Van Dyke</a>, <a href="/search/quant-ph?searchtype=author&query=Shirali%2C+K">Karunya Shirali</a>, <a href="/search/quant-ph?searchtype=author&query=Barron%2C+G+S">George S. Barron</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2206.14215v2-abstract-short" style="display: inline;"> Adaptive variational quantum simulation algorithms use information from the quantum computer to dynamically create optimal trial wavefunctions for a given problem Hamiltonian. A key ingredient in these algorithms is a predefined operator pool from which trial wavefunctions are constructed. Finding suitable pools is critical for the efficiency of the algorithm as the problem size increases. Here, w… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2206.14215v2-abstract-full').style.display = 'inline'; document.getElementById('2206.14215v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2206.14215v2-abstract-full" style="display: none;"> Adaptive variational quantum simulation algorithms use information from the quantum computer to dynamically create optimal trial wavefunctions for a given problem Hamiltonian. A key ingredient in these algorithms is a predefined operator pool from which trial wavefunctions are constructed. Finding suitable pools is critical for the efficiency of the algorithm as the problem size increases. Here, we present a technique called operator pool tiling that facilitates the construction of problem-tailored pools for arbitrarily large problem instances. By first performing an ADAPT-VQE calculation on a smaller instance of the problem using a large, but computationally inefficient operator pool, we extract the most relevant operators and use them to design more efficient pools for larger instances. We demonstrate the method here on strongly correlated quantum spin models in one and two dimensions, finding that ADAPT automatically finds a highly effective ansatz for these systems. Given that many problems, such as those arising in condensed matter physics, have a naturally repeating lattice structure, we expect the pool tiling method to be a widely applicable technique apt for such systems. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2206.14215v2-abstract-full').style.display = 'none'; document.getElementById('2206.14215v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 November, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 28 June, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, 4 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2206.10502">arXiv:2206.10502</a> <span> [<a href="https://arxiv.org/pdf/2206.10502">pdf</a>, <a href="https://arxiv.org/format/2206.10502">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Strongly Correlated Electrons">cond-mat.str-el</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Chemical Physics">physics.chem-ph</span> </div> </div> <p class="title is-5 mathjax"> Quantum self-consistent equation-of-motion method for computing molecular excitation energies, ionization potentials, and electron affinities on a quantum computer </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Asthana%2C+A">Ayush Asthana</a>, <a href="/search/quant-ph?searchtype=author&query=Kumar%2C+A">Ashutosh Kumar</a>, <a href="/search/quant-ph?searchtype=author&query=Abraham%2C+V">Vibin Abraham</a>, <a href="/search/quant-ph?searchtype=author&query=Grimsley%2C+H">Harper Grimsley</a>, <a href="/search/quant-ph?searchtype=author&query=Zhang%2C+Y">Yu Zhang</a>, <a href="/search/quant-ph?searchtype=author&query=Cincio%2C+L">Lukasz Cincio</a>, <a href="/search/quant-ph?searchtype=author&query=Tretiak%2C+S">Sergei Tretiak</a>, <a href="/search/quant-ph?searchtype=author&query=Dub%2C+P+A">Pavel A. Dub</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2206.10502v2-abstract-short" style="display: inline;"> Near-term quantum computers are expected to facilitate material and chemical research through accurate molecular simulations. Several developments have already shown that accurate ground-state energies for small molecules can be evaluated on present-day quantum devices. Although electronically excited states play a vital role in chemical processes and applications, the search for a reliable and pr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2206.10502v2-abstract-full').style.display = 'inline'; document.getElementById('2206.10502v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2206.10502v2-abstract-full" style="display: none;"> Near-term quantum computers are expected to facilitate material and chemical research through accurate molecular simulations. Several developments have already shown that accurate ground-state energies for small molecules can be evaluated on present-day quantum devices. Although electronically excited states play a vital role in chemical processes and applications, the search for a reliable and practical approach for routine excited-state calculations on near-term quantum devices is ongoing. Inspired by excited-state methods developed for the unitary coupled-cluster theory in quantum chemistry, we present an equation-of-motion-based method to compute excitation energies following the variational quantum eigensolver algorithm for ground-state calculations on a quantum computer. We perform numerical simulations on H$_2$, H$_4$, H$_2$O, and LiH molecules to test our quantum self-consistent equation-of-motion (q-sc-EOM) method and compare it to other current state-of-the-art methods. q-sc-EOM makes use of self-consistent operators to satisfy the vacuum annihilation condition, a critical property for accurate calculations. It provides real and size-intensive energy differences corresponding to vertical excitation energies, ionization potentials and electron affinities. We also find that q-sc-EOM is more suitable for implementation on NISQ devices as it is expected to be more resilient to noise compared with the currently available methods. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2206.10502v2-abstract-full').style.display = 'none'; document.getElementById('2206.10502v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 February, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 21 June, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Report number:</span> LA-UR-22-25463 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2205.12283">arXiv:2205.12283</a> <span> [<a href="https://arxiv.org/pdf/2205.12283">pdf</a>, <a href="https://arxiv.org/format/2205.12283">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> How Much Entanglement Do Quantum Optimization Algorithms Require? </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Chen%2C+Y">Yanzhu Chen</a>, <a href="/search/quant-ph?searchtype=author&query=Zhu%2C+L">Linghua Zhu</a>, <a href="/search/quant-ph?searchtype=author&query=Liu%2C+C">Chenxu Liu</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2205.12283v2-abstract-short" style="display: inline;"> Many classical optimization problems can be mapped to finding the ground states of diagonal Ising Hamiltonians, for which variational quantum algorithms such as the Quantum Approximate Optimization Algorithm (QAOA) provide heuristic methods. Because the solutions of such classical optimization problems are necessarily product states, it is unclear how entanglement affects their performance. An Ada… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.12283v2-abstract-full').style.display = 'inline'; document.getElementById('2205.12283v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2205.12283v2-abstract-full" style="display: none;"> Many classical optimization problems can be mapped to finding the ground states of diagonal Ising Hamiltonians, for which variational quantum algorithms such as the Quantum Approximate Optimization Algorithm (QAOA) provide heuristic methods. Because the solutions of such classical optimization problems are necessarily product states, it is unclear how entanglement affects their performance. An Adaptive Derivative-Assembled Problem-Tailored (ADAPT) variation of QAOA improves the convergence rate by allowing entangling operations in the mixer layers whereas it requires fewer CNOT gates in the entire circuit. In this work, we study the entanglement generated during the execution of ADAPT-QAOA. Through simulations of the weighted Max-Cut problem, we show that ADAPT-QAOA exhibits substantial flexibility in entangling and disentangling qubits. By incrementally restricting this flexibility, we find that a larger amount of entanglement entropy at earlier stages coincides with faster convergence at later stages. In contrast, while the standard QAOA quickly generates entanglement within a few layers, it cannot remove excess entanglement efficiently. Our results demonstrate that the role of entanglement in quantum optimization is subtle and provide guidance for building favorable features into quantum optimization algorithms. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.12283v2-abstract-full').style.display = 'none'; document.getElementById('2205.12283v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 9 July, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 24 May, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 7 figures. Comments are welcome</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2204.07179">arXiv:2204.07179</a> <span> [<a href="https://arxiv.org/pdf/2204.07179">pdf</a>, <a href="https://arxiv.org/format/2204.07179">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Chemical Physics">physics.chem-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1038/s41534-023-00681-0">10.1038/s41534-023-00681-0 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> ADAPT-VQE is insensitive to rough parameter landscapes and barren plateaus </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Grimsley%2C+H+R">Harper R. Grimsley</a>, <a href="/search/quant-ph?searchtype=author&query=Barron%2C+G+S">George S. Barron</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2204.07179v1-abstract-short" style="display: inline;"> Variational quantum eigensolvers (VQEs) represent a powerful class of hybrid quantum-classical algorithms for computing molecular energies. Various numerical issues exist for these methods, however, including barren plateaus and large numbers of local minima. In this work, we consider Adaptive, Problem-Tailored (ADAPT)-VQE ans盲tze, and examine how they are impacted by these local minima. We find t… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2204.07179v1-abstract-full').style.display = 'inline'; document.getElementById('2204.07179v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2204.07179v1-abstract-full" style="display: none;"> Variational quantum eigensolvers (VQEs) represent a powerful class of hybrid quantum-classical algorithms for computing molecular energies. Various numerical issues exist for these methods, however, including barren plateaus and large numbers of local minima. In this work, we consider Adaptive, Problem-Tailored (ADAPT)-VQE ans盲tze, and examine how they are impacted by these local minima. We find that while ADAPT-VQE does not remove local minima, the gradient-informed, one-operator-at-a-time circuit construction seems to accomplish two things: First, it provides an initialization strategy that is dramatically better than random initialization, and which is applicable in situations where chemical intuition cannot help with initialization, i.e., when Hartree-Fock is a poor approximation to the ground state. Second, even if an ADAPT-VQE iteration converges to a local trap at one step, it can still "burrow" toward the exact solution by adding more operators, which preferentially deepens the occupied trap. This same mechanism helps highlight a surprising feature of ADAPT-VQE: It should not suffer optimization problems due to "barren plateaus". Even if barren plateaus appear in the parameter landscape, our analysis and simulations reveal that ADAPT-VQE avoids such regions by design. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2204.07179v1-abstract-full').style.display = 'none'; document.getElementById('2204.07179v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 14 April, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2022. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2204.02876">arXiv:2204.02876</a> <span> [<a href="https://arxiv.org/pdf/2204.02876">pdf</a>, <a href="https://arxiv.org/format/2204.02876">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevApplied.19.044094">10.1103/PhysRevApplied.19.044094 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Designing globally optimal entangling gates using geometric space curves </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Tang%2C+H+L">Ho Lun Tang</a>, <a href="/search/quant-ph?searchtype=author&query=Connelly%2C+K">Kyle Connelly</a>, <a href="/search/quant-ph?searchtype=author&query=Warren%2C+A">Ada Warren</a>, <a href="/search/quant-ph?searchtype=author&query=Zhuang%2C+F">Fei Zhuang</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2204.02876v1-abstract-short" style="display: inline;"> High-fidelity entangling gates are essential for quantum computation. Currently, most approaches to designing such gates are based either on simple, analytical pulse waveforms or on ones obtained from numerical optimization techniques. In both cases, it is typically not possible to obtain a global understanding of the space of waveforms that generate a target gate operation, making it challenging… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2204.02876v1-abstract-full').style.display = 'inline'; document.getElementById('2204.02876v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2204.02876v1-abstract-full" style="display: none;"> High-fidelity entangling gates are essential for quantum computation. Currently, most approaches to designing such gates are based either on simple, analytical pulse waveforms or on ones obtained from numerical optimization techniques. In both cases, it is typically not possible to obtain a global understanding of the space of waveforms that generate a target gate operation, making it challenging to design globally optimal gates. Here, we show that in the case of weakly coupled qubits, it is possible to find all pulses that implement a target entangling gate. We do this by mapping quantum evolution onto geometric space curves. We derive the minimal conditions these curves must satisfy in order to guarantee a gate with a desired entangling power is implemented. Pulse waveforms are extracted from the curvatures of these curves. We illustrate our method by designing fast, CNOT-equivalent entangling gates for silicon quantum dot spin qubits with fidelities exceeding 99%. We show that fidelities can be further improved while maintaining low bandwidth requirements by using geometrically derived pulses as initial guesses in numerical optimization routines. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2204.02876v1-abstract-full').style.display = 'none'; document.getElementById('2204.02876v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 6 April, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, 3 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. Applied 19, 044094 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2203.12757">arXiv:2203.12757</a> <span> [<a href="https://arxiv.org/pdf/2203.12757">pdf</a>, <a href="https://arxiv.org/ps/2203.12757">ps</a>, <a href="https://arxiv.org/format/2203.12757">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Adaptive variational algorithms for quantum Gibbs state preparation </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Warren%2C+A">Ada Warren</a>, <a href="/search/quant-ph?searchtype=author&query=Zhu%2C+L">Linghua Zhu</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2203.12757v1-abstract-short" style="display: inline;"> The preparation of Gibbs thermal states is an important task in quantum computation with applications in quantum simulation, quantum optimization, and quantum machine learning. However, many algorithms for preparing Gibbs states rely on quantum subroutines which are difficult to implement on near-term hardware. Here, we address this by (i) introducing an objective function that, unlike the free en… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.12757v1-abstract-full').style.display = 'inline'; document.getElementById('2203.12757v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2203.12757v1-abstract-full" style="display: none;"> The preparation of Gibbs thermal states is an important task in quantum computation with applications in quantum simulation, quantum optimization, and quantum machine learning. However, many algorithms for preparing Gibbs states rely on quantum subroutines which are difficult to implement on near-term hardware. Here, we address this by (i) introducing an objective function that, unlike the free energy, is easily measured, and (ii) using dynamically generated, problem-tailored ans盲tze. This allows for arbitrarily accurate Gibbs state preparation using low-depth circuits. To verify the effectiveness of our approach, we numerically demonstrate that our algorithm can prepare high-fidelity Gibbs states across a broad range of temperatures and for a variety of Hamiltonians. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.12757v1-abstract-full').style.display = 'none'; document.getElementById('2203.12757v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 March, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">7 pages, 3 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2203.09459">arXiv:2203.09459</a> <span> [<a href="https://arxiv.org/pdf/2203.09459">pdf</a>, <a href="https://arxiv.org/format/2203.09459">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevX.13.011004">10.1103/PhysRevX.13.011004 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Precise control of entanglement in multinuclear spin registers coupled to defects </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Takou%2C+E">Evangelia Takou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2203.09459v2-abstract-short" style="display: inline;"> Quantum networks play an indispensable role in quantum information tasks such as secure communications, enhanced quantum sensing, and distributed computing. Among the most mature and promising platforms for quantum networking are nitrogen-vacancy centers in diamond and other color centers in solids. One of the challenges in using these systems for networking applications is to controllably manipul… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.09459v2-abstract-full').style.display = 'inline'; document.getElementById('2203.09459v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2203.09459v2-abstract-full" style="display: none;"> Quantum networks play an indispensable role in quantum information tasks such as secure communications, enhanced quantum sensing, and distributed computing. Among the most mature and promising platforms for quantum networking are nitrogen-vacancy centers in diamond and other color centers in solids. One of the challenges in using these systems for networking applications is to controllably manipulate entanglement between the electron and the nuclear spin register despite the always-on nature of the hyperfine interactions, which makes this an inherently many-body quantum system. Here, we develop a general formalism to quantify and control the generation of entanglement in an arbitrarily large nuclear spin register coupled to a color center electronic spin. We provide a reliable measure of nuclear spin selectivity, by exactly incorporating into our treatment the dynamics with unwanted nuclei. We also show how to realize direct multipartite gates through the use of dynamical decoupling sequences, drastically reducing the total gate time compared to protocols based on sequential entanglement with individual nuclear spins. We quantify the performance of such gate operations in the presence of unwanted residual entanglement links, capturing the dynamics of the entire nuclear spin register. Finally, using experimental parameters of a well-characterized 27 nuclear spin register device, we show how to prepare with high fidelity entangled states for quantum error correction. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.09459v2-abstract-full').style.display = 'none'; document.getElementById('2203.09459v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 17 May, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 17 March, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17+18 pages, 16 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. X 13, 011004 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2203.07210">arXiv:2203.07210</a> <span> [<a href="https://arxiv.org/pdf/2203.07210">pdf</a>, <a href="https://arxiv.org/format/2203.07210">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevResearch.5.023124">10.1103/PhysRevResearch.5.023124 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Extracting perfect GHZ states from imperfect weighted graph states via entanglement concentration </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Frantzeskakis%2C+R">Rafail Frantzeskakis</a>, <a href="/search/quant-ph?searchtype=author&query=Liu%2C+C">Chenxu Liu</a>, <a href="/search/quant-ph?searchtype=author&query=Raissi%2C+Z">Zahra Raissi</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2203.07210v2-abstract-short" style="display: inline;"> Photonic GHZ states serve as the central resource for a number of important applications in quantum information science, including secret sharing, sensing, and fusion-based quantum computing. The use of photon-emitter entangling gates is a promising approach to creating these states that sidesteps many of the difficulties associated with intrinsically probabilistic methods based on linear optics.… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.07210v2-abstract-full').style.display = 'inline'; document.getElementById('2203.07210v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2203.07210v2-abstract-full" style="display: none;"> Photonic GHZ states serve as the central resource for a number of important applications in quantum information science, including secret sharing, sensing, and fusion-based quantum computing. The use of photon-emitter entangling gates is a promising approach to creating these states that sidesteps many of the difficulties associated with intrinsically probabilistic methods based on linear optics. However, the efficient creation of high-fidelity GHZ states of many photons remains an outstanding challenge due to both coherent and incoherent errors during the generation process. Here, we propose an entanglement concentration protocol that is capable of generating perfect GHZ states using only local gates and measurements on imperfect weighted graph states. We show that our protocol is both efficient and robust to incoherent noise errors. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.07210v2-abstract-full').style.display = 'none'; document.getElementById('2203.07210v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 24 December, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 14 March, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages, 8 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. Research 5, 023124 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2203.06818">arXiv:2203.06818</a> <span> [<a href="https://arxiv.org/pdf/2203.06818">pdf</a>, <a href="https://arxiv.org/format/2203.06818">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Chemical Physics">physics.chem-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevApplied.19.064071">10.1103/PhysRevApplied.19.064071 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Minimizing state preparation times in pulse-level variational molecular simulations </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Asthana%2C+A">Ayush Asthana</a>, <a href="/search/quant-ph?searchtype=author&query=Liu%2C+C">Chenxu Liu</a>, <a href="/search/quant-ph?searchtype=author&query=Meitei%2C+O+R">Oinam Romesh Meitei</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2203.06818v1-abstract-short" style="display: inline;"> Quantum simulation on NISQ devices is severely limited by short coherence times. A variational pulse-shaping algorithm known as ctrl-VQE was recently proposed to address this issue by eliminating the need for parameterized quantum circuits, which lead to long state preparation times. Here, we find the shortest possible pulses for ctrl-VQE to prepare target molecular wavefunctions for a given devic… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.06818v1-abstract-full').style.display = 'inline'; document.getElementById('2203.06818v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2203.06818v1-abstract-full" style="display: none;"> Quantum simulation on NISQ devices is severely limited by short coherence times. A variational pulse-shaping algorithm known as ctrl-VQE was recently proposed to address this issue by eliminating the need for parameterized quantum circuits, which lead to long state preparation times. Here, we find the shortest possible pulses for ctrl-VQE to prepare target molecular wavefunctions for a given device Hamiltonian describing coupled transmon qubits. We find that the time-optimal pulses that do this have a bang-bang form consistent with Pontryagin's maximum principle. We further investigate how the minimal state preparation time is impacted by truncating the transmons to two versus more levels. We find that leakage outside the computational subspace (something that is usually considered problematic) speeds up the state preparation, further reducing device coherence-time demands. This speedup is due to an enlarged solution space of target wavefunctions and to the appearance of additional channels connecting initial and target states. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.06818v1-abstract-full').style.display = 'none'; document.getElementById('2203.06818v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 13 March, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. Applied 19, 064071 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2201.00836">arXiv:2201.00836</a> <span> [<a href="https://arxiv.org/pdf/2201.00836">pdf</a>, <a href="https://arxiv.org/format/2201.00836">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Proposal for generating complex microwave graph states using superconducting circuits </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Liu%2C+C">Chenxu Liu</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S">Sophia Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2201.00836v1-abstract-short" style="display: inline;"> Microwave photonic graph states provide a promising approach for robust quantum communication between remote superconducting chips using microwave photons. Recently, Besse et al. [Nat. Commun. 11, 4887 (2020)] demonstrated that 1D graph states can be generated using two transmon qubits. In this paper, we propose to use transmon qubits combined with other microwave devices to construct more complex… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2201.00836v1-abstract-full').style.display = 'inline'; document.getElementById('2201.00836v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2201.00836v1-abstract-full" style="display: none;"> Microwave photonic graph states provide a promising approach for robust quantum communication between remote superconducting chips using microwave photons. Recently, Besse et al. [Nat. Commun. 11, 4887 (2020)] demonstrated that 1D graph states can be generated using two transmon qubits. In this paper, we propose to use transmon qubits combined with other microwave devices to construct more complex graph states. Specifically, we consider 2D lattice and tree-like graph states. We compare the performance using fixed- versus tunable-frequency transmon qubits and also for different photonic qubit encodings. In each case, we estimate the fidelity of the resulting microwave graph state assuming current experimental parameters and identify the main factors that limit performance. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2201.00836v1-abstract-full').style.display = 'none'; document.getElementById('2201.00836v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 3 January, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 10 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2111.08045">arXiv:2111.08045</a> <span> [<a href="https://arxiv.org/pdf/2111.08045">pdf</a>, <a href="https://arxiv.org/format/2111.08045">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevA.106.062424">10.1103/PhysRevA.106.062424 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> General stabilizer approach for constructing highly entangled graph states </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Raissi%2C+Z">Zahra Raissi</a>, <a href="/search/quant-ph?searchtype=author&query=Burchardt%2C+A">Adam Burchardt</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2111.08045v2-abstract-short" style="display: inline;"> Highly entangled multipartite states such as k-uniform (k-UNI) and absolutely maximally entangled (AME) states serve as critical resources in quantum networking and other quantum information applications. However, there does not yet exist a complete classification of such states, and much remains unknown about their entanglement structure. Here, we substantially broaden the class of known k-UNI an… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2111.08045v2-abstract-full').style.display = 'inline'; document.getElementById('2111.08045v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2111.08045v2-abstract-full" style="display: none;"> Highly entangled multipartite states such as k-uniform (k-UNI) and absolutely maximally entangled (AME) states serve as critical resources in quantum networking and other quantum information applications. However, there does not yet exist a complete classification of such states, and much remains unknown about their entanglement structure. Here, we substantially broaden the class of known k-UNI and AME states by introducing a method for explicitly constructing such states that combines classical error correcting codes and qudit graph states. This method in fact constitutes a general recipe for obtaining multipartitite entangled states from classical codes. Furthermore, we show that at least for a large subset of this new class of k-UNI states, the states are inequivalent under stochastic local operations and classical communication. This subset is defined by an iterative procedure for constructing a hierarchy of k-UNI graph states. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2111.08045v2-abstract-full').style.display = 'none'; document.getElementById('2111.08045v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 21 November, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 15 November, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, 3 figures. Comments are very welcome!</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2109.05607">arXiv:2109.05607</a> <span> [<a href="https://arxiv.org/pdf/2109.05607">pdf</a>, <a href="https://arxiv.org/format/2109.05607">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/1751-8121/ac4640">10.1088/1751-8121/ac4640 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Preparing exact eigenstates of the open XXZ chain on a quantum computer </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Van+Dyke%2C+J+S">John S. Van Dyke</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Nepomechie%2C+R+I">Rafael I. Nepomechie</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2109.05607v2-abstract-short" style="display: inline;"> The open spin-1/2 XXZ spin chain with diagonal boundary magnetic fields is the paradigmatic example of a quantum integrable model with open boundary conditions. We formulate a quantum algorithm for preparing Bethe states of this model, corresponding to real solutions of the Bethe equations. The algorithm is probabilistic, with a success probability that decreases with the number of down spins. For… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.05607v2-abstract-full').style.display = 'inline'; document.getElementById('2109.05607v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2109.05607v2-abstract-full" style="display: none;"> The open spin-1/2 XXZ spin chain with diagonal boundary magnetic fields is the paradigmatic example of a quantum integrable model with open boundary conditions. We formulate a quantum algorithm for preparing Bethe states of this model, corresponding to real solutions of the Bethe equations. The algorithm is probabilistic, with a success probability that decreases with the number of down spins. For a Bethe state of $L$ spins with $M$ down spins, which contains a total of $\binom{L}{M}\, 2^{M}\, M!$ terms, the algorithm requires $L+M^2+2M$ qubits. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.05607v2-abstract-full').style.display = 'none'; document.getElementById('2109.05607v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 December, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 12 September, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 3 figures; v2: references added and further minor improvements - to appear in J. Phys. A</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Report number:</span> UMTG-312 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2109.05340">arXiv:2109.05340</a> <span> [<a href="https://arxiv.org/pdf/2109.05340">pdf</a>, <a href="https://arxiv.org/format/2109.05340">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.22331/q-2023-06-12-1040">10.22331/q-2023-06-12-1040 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Avoiding symmetry roadblocks and minimizing the measurement overhead of adaptive variational quantum eigensolvers </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Shkolnikov%2C+V+O">V. O. Shkolnikov</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2109.05340v2-abstract-short" style="display: inline;"> Quantum simulation of strongly correlated systems is potentially the most feasible useful application of near-term quantum computers. Minimizing quantum computational resources is crucial to achieving this goal. A promising class of algorithms for this purpose consists of variational quantum eigensolvers (VQEs). Among these, problem-tailored versions such as ADAPT-VQE that build variational ans盲tz… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.05340v2-abstract-full').style.display = 'inline'; document.getElementById('2109.05340v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2109.05340v2-abstract-full" style="display: none;"> Quantum simulation of strongly correlated systems is potentially the most feasible useful application of near-term quantum computers. Minimizing quantum computational resources is crucial to achieving this goal. A promising class of algorithms for this purpose consists of variational quantum eigensolvers (VQEs). Among these, problem-tailored versions such as ADAPT-VQE that build variational ans盲tze step by step from a predefined operator pool perform particularly well in terms of circuit depths and variational parameter counts. However, this improved performance comes at the expense of an additional measurement overhead compared to standard VQEs. Here, we show that this overhead can be reduced to an amount that grows only linearly with the number $n$ of qubits, instead of quartically as in the original ADAPT-VQE. We do this by proving that operator pools of size $2n-2$ can represent any state in Hilbert space if chosen appropriately. We prove that this is the minimal size of such "complete" pools, discuss their algebraic properties, and present necessary and sufficient conditions for their completeness that allow us to find such pools efficiently. We further show that, if the simulated problem possesses symmetries, then complete pools can fail to yield convergent results, unless the pool is chosen to obey certain symmetry rules. We demonstrate the performance of such symmetry-adapted complete pools by using them in classical simulations of ADAPT-VQE for several strongly correlated molecules. Our findings are relevant for any VQE that uses an ansatz based on Pauli strings. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2109.05340v2-abstract-full').style.display = 'none'; document.getElementById('2109.05340v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 6 June, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 11 September, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15+10 pages, 7 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Quantum 7, 1040 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2108.12466">arXiv:2108.12466</a> <span> [<a href="https://arxiv.org/pdf/2108.12466">pdf</a>, <a href="https://arxiv.org/format/2108.12466">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1038/s41534-022-00522-6">10.1038/s41534-022-00522-6 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Photonic resource state generation from a minimal number of quantum emitters </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Li%2C+B">Bikun Li</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2108.12466v2-abstract-short" style="display: inline;"> Multi-photon entangled graph states are a fundamental resource in quantum communication networks, distributed quantum computing, and sensing. These states can in principle be created deterministically from quantum emitters such as optically active quantum dots or defects, atomic systems, or superconducting qubits. However, finding efficient schemes to produce such states has been a long-standing c… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2108.12466v2-abstract-full').style.display = 'inline'; document.getElementById('2108.12466v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2108.12466v2-abstract-full" style="display: none;"> Multi-photon entangled graph states are a fundamental resource in quantum communication networks, distributed quantum computing, and sensing. These states can in principle be created deterministically from quantum emitters such as optically active quantum dots or defects, atomic systems, or superconducting qubits. However, finding efficient schemes to produce such states has been a long-standing challenge. Here, we present an algorithm that, given a desired multi-photon graph state, determines the minimum number of quantum emitters and precise operation sequences that can produce it. The algorithm itself and the resulting operation sequence both scale polynomially in the size of the photonic graph state, allowing one to obtain efficient schemes to generate graph states containing hundreds or thousands of photons. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2108.12466v2-abstract-full').style.display = 'none'; document.getElementById('2108.12466v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 20 August, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 27 August, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">14 pages, 8 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2103.16015">arXiv:2103.16015</a> <span> [<a href="https://arxiv.org/pdf/2103.16015">pdf</a>, <a href="https://arxiv.org/format/2103.16015">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> Dynamically corrected gates from geometric space curves </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Calderon-Vargas%2C+F+A">Fernando A. Calderon-Vargas</a>, <a href="/search/quant-ph?searchtype=author&query=Dong%2C+W">Wenzheng Dong</a>, <a href="/search/quant-ph?searchtype=author&query=Li%2C+B">Bikun Li</a>, <a href="/search/quant-ph?searchtype=author&query=Zeng%2C+J">Junkai Zeng</a>, <a href="/search/quant-ph?searchtype=author&query=Zhuang%2C+F">Fei Zhuang</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2103.16015v1-abstract-short" style="display: inline;"> Quantum information technologies demand highly accurate control over quantum systems. Achieving this requires control techniques that perform well despite the presence of decohering noise and other adverse effects. Here, we review a general technique for designing control fields that dynamically correct errors while performing operations using a close relationship between quantum evolution and geo… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.16015v1-abstract-full').style.display = 'inline'; document.getElementById('2103.16015v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2103.16015v1-abstract-full" style="display: none;"> Quantum information technologies demand highly accurate control over quantum systems. Achieving this requires control techniques that perform well despite the presence of decohering noise and other adverse effects. Here, we review a general technique for designing control fields that dynamically correct errors while performing operations using a close relationship between quantum evolution and geometric space curves. This approach provides access to the global solution space of control fields that accomplish a given task, facilitating the design of experimentally feasible gate operations for a wide variety of applications. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.16015v1-abstract-full').style.display = 'none'; document.getElementById('2103.16015v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 29 March, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">25 pages, 17 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2103.13388">arXiv:2103.13388</a> <span> [<a href="https://arxiv.org/pdf/2103.13388">pdf</a>, <a href="https://arxiv.org/format/2103.13388">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PRXQuantum.2.040329">10.1103/PRXQuantum.2.040329 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Preparing Bethe Ansatz Eigenstates on a Quantum Computer </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Van+Dyke%2C+J+S">John S. Van Dyke</a>, <a href="/search/quant-ph?searchtype=author&query=Barron%2C+G+S">George S. Barron</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2103.13388v3-abstract-short" style="display: inline;"> Several quantum many-body models in one dimension possess exact solutions via the Bethe ansatz method, which has been highly successful for understanding their behavior. Nevertheless, there remain physical properties of such models for which analytic results are unavailable, and which are also not well-described by approximate numerical methods. Preparing Bethe ansatz eigenstates directly on a qua… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.13388v3-abstract-full').style.display = 'inline'; document.getElementById('2103.13388v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2103.13388v3-abstract-full" style="display: none;"> Several quantum many-body models in one dimension possess exact solutions via the Bethe ansatz method, which has been highly successful for understanding their behavior. Nevertheless, there remain physical properties of such models for which analytic results are unavailable, and which are also not well-described by approximate numerical methods. Preparing Bethe ansatz eigenstates directly on a quantum computer would allow straightforward extraction of these quantities via measurement. We present a quantum algorithm for preparing Bethe ansatz eigenstates of the spin-1/2 XXZ spin chain that correspond to real-valued solutions of the Bethe equations. The algorithm is polynomial in the number of T gates and circuit depth, with modest constant prefactors. Although the algorithm is probabilistic, with a success rate that decreases with increasing eigenstate energy, we employ amplitude amplification to boost the success probability. The resource requirements for our approach are lower than other state-of-the-art quantum simulation algorithms for small error-corrected devices, and thus may offer an alternative and computationally less-demanding demonstration of quantum advantage for physically relevant problems. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.13388v3-abstract-full').style.display = 'none'; document.getElementById('2103.13388v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 24 November, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 24 March, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">14 pages, 9 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> PRX Quantum 2, 040329 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2103.12305">arXiv:2103.12305</a> <span> [<a href="https://arxiv.org/pdf/2103.12305">pdf</a>, <a href="https://arxiv.org/format/2103.12305">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> </div> <p class="title is-5 mathjax"> A universal quantum gate set for transmon qubits with strong ZZ interactions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Long%2C+J">Junling Long</a>, <a href="/search/quant-ph?searchtype=author&query=Zhao%2C+T">Tongyu Zhao</a>, <a href="/search/quant-ph?searchtype=author&query=Bal%2C+M">Mustafa Bal</a>, <a href="/search/quant-ph?searchtype=author&query=Zhao%2C+R">Ruichen Zhao</a>, <a href="/search/quant-ph?searchtype=author&query=Barron%2C+G+S">George S. Barron</a>, <a href="/search/quant-ph?searchtype=author&query=Ku%2C+H">Hsiang-sheng Ku</a>, <a href="/search/quant-ph?searchtype=author&query=Howard%2C+J+A">Joel A. Howard</a>, <a href="/search/quant-ph?searchtype=author&query=Wu%2C+X">Xian Wu</a>, <a href="/search/quant-ph?searchtype=author&query=McRae%2C+C+R+H">Corey Rae H. McRae</a>, <a href="/search/quant-ph?searchtype=author&query=Deng%2C+X">Xiu-Hao Deng</a>, <a href="/search/quant-ph?searchtype=author&query=Ribeill%2C+G+J">Guilhem J. Ribeill</a>, <a href="/search/quant-ph?searchtype=author&query=Singh%2C+M">Meenakshi Singh</a>, <a href="/search/quant-ph?searchtype=author&query=Ohki%2C+T+A">Thomas A. Ohki</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Pappas%2C+D+P">David P. Pappas</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2103.12305v1-abstract-short" style="display: inline;"> High-fidelity single- and two-qubit gates are essential building blocks for a fault-tolerant quantum computer. While there has been much progress in suppressing single-qubit gate errors in superconducting qubit systems, two-qubit gates still suffer from error rates that are orders of magnitude higher. One limiting factor is the residual ZZ-interaction, which originates from a coupling between comp… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.12305v1-abstract-full').style.display = 'inline'; document.getElementById('2103.12305v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2103.12305v1-abstract-full" style="display: none;"> High-fidelity single- and two-qubit gates are essential building blocks for a fault-tolerant quantum computer. While there has been much progress in suppressing single-qubit gate errors in superconducting qubit systems, two-qubit gates still suffer from error rates that are orders of magnitude higher. One limiting factor is the residual ZZ-interaction, which originates from a coupling between computational states and higher-energy states. While this interaction is usually viewed as a nuisance, here we experimentally demonstrate that it can be exploited to produce a universal set of fast single- and two-qubit entangling gates in a coupled transmon qubit system. To implement arbitrary single-qubit rotations, we design a new protocol called the two-axis gate that is based on a three-part composite pulse. It rotates a single qubit independently of the state of the other qubit despite the strong ZZ-coupling. We achieve single-qubit gate fidelities as high as 99.1% from randomized benchmarking measurements. We then demonstrate both a CZ gate and a CNOT gate. Because the system has a strong ZZ-interaction, a CZ gate can be achieved by letting the system freely evolve for a gate time $t_g=53.8$ ns. To design the CNOT gate, we utilize an analytical microwave pulse shape based on the SWIPHT protocol for realizing fast, low-leakage gates. We obtain fidelities of 94.6% and 97.8% for the CNOT and CZ gates respectively from quantum progress tomography. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.12305v1-abstract-full').style.display = 'none'; document.getElementById('2103.12305v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 March, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2021. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2103.08506">arXiv:2103.08506</a> <span> [<a href="https://arxiv.org/pdf/2103.08506">pdf</a>, <a href="https://arxiv.org/format/2103.08506">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/1367-2630/ac22ea">10.1088/1367-2630/ac22ea <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Designing arbitrary single-axis rotations robust against perpendicular time-dependent noise </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Li%2C+B">Bikun Li</a>, <a href="/search/quant-ph?searchtype=author&query=Calderon-Vargas%2C+F+A">F. A. Calderon-Vargas</a>, <a href="/search/quant-ph?searchtype=author&query=Zeng%2C+J">Junkai Zeng</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2103.08506v1-abstract-short" style="display: inline;"> Low-frequency time-dependent noise is one of the main obstacles on the road towards a fully scalable quantum computer. The majority of solid-state qubit platforms, from superconducting circuits to spins in semiconductors, are greatly affected by $1/f$ noise. Among the different control techniques used to counteract noise effects on the system, dynamical decoupling sequences are one of the most eff… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.08506v1-abstract-full').style.display = 'inline'; document.getElementById('2103.08506v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2103.08506v1-abstract-full" style="display: none;"> Low-frequency time-dependent noise is one of the main obstacles on the road towards a fully scalable quantum computer. The majority of solid-state qubit platforms, from superconducting circuits to spins in semiconductors, are greatly affected by $1/f$ noise. Among the different control techniques used to counteract noise effects on the system, dynamical decoupling sequences are one of the most effective. However, most dynamical decoupling sequences require unbounded and instantaneous pulses, which are unphysical and can only implement identity operations. Among methods that do restrict to bounded control fields, there remains a need for protocols that implement arbitrary gates with lab-ready control fields. In this work, we introduce a protocol to design bounded and continuous control fields that implement arbitrary single-axis rotations while shielding the system from low-frequency time-dependent noise perpendicular to the control axis. We show the versatility of our method by presenting a set of non-negative-only control pulses that are immediately applicable to quantum systems with constrained control, such as singlet-triplet spin qubits. Finally, we demonstrate the robustness of our control pulses against classical $1/f$ noise and noise modeled with a random quantum bath, showing that our pulses can even outperform ideal dynamical decoupling sequences. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.08506v1-abstract-full').style.display = 'none'; document.getElementById('2103.08506v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 15 March, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages, 4 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2103.08029">arXiv:2103.08029</a> <span> [<a href="https://arxiv.org/pdf/2103.08029">pdf</a>, <a href="https://arxiv.org/format/2103.08029">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PRXQuantum.2.030333">10.1103/PRXQuantum.2.030333 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Doubly geometric quantum control </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Dong%2C+W">Wenzheng Dong</a>, <a href="/search/quant-ph?searchtype=author&query=Zhuang%2C+F">Fei Zhuang</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2103.08029v2-abstract-short" style="display: inline;"> In holonomic quantum computation, single-qubit gates are performed using driving protocols that trace out closed loops on the Bloch sphere, making them robust to certain pulse errors. However, dephasing noise that is transverse to the drive, which is significant in many qubit platforms, lies outside the family of correctable errors. Here, we present a general procedure that combines two types of g… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.08029v2-abstract-full').style.display = 'inline'; document.getElementById('2103.08029v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2103.08029v2-abstract-full" style="display: none;"> In holonomic quantum computation, single-qubit gates are performed using driving protocols that trace out closed loops on the Bloch sphere, making them robust to certain pulse errors. However, dephasing noise that is transverse to the drive, which is significant in many qubit platforms, lies outside the family of correctable errors. Here, we present a general procedure that combines two types of geometry -- holonomy loops on the Bloch sphere and geometric space curves in three dimensions -- to design gates that simultaneously suppress pulse errors and transverse noise errors. We demonstrate this doubly geometric control technique by designing explicit examples of such dynamically corrected holonomic gates. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.08029v2-abstract-full').style.display = 'none'; document.getElementById('2103.08029v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 20 July, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 14 March, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 13 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> PRX Quantum 2, 030333 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2103.07586">arXiv:2103.07586</a> <span> [<a href="https://arxiv.org/pdf/2103.07586">pdf</a>, <a href="https://arxiv.org/format/2103.07586">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.22331/q-2022-02-02-639">10.22331/q-2022-02-02-639 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Noise-resistant Landau-Zener sweeps from geometrical curves </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Zhuang%2C+F">Fei Zhuang</a>, <a href="/search/quant-ph?searchtype=author&query=Zeng%2C+J">Junkai Zeng</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2103.07586v3-abstract-short" style="display: inline;"> Landau-Zener physics is often exploited to generate quantum logic gates and to perform state initialization and readout. The quality of these operations can be degraded by noise fluctuations in the energy gap at the avoided crossing. We leverage a recently discovered correspondence between qubit evolution and space curves in three dimensions to design noise-robust Landau-Zener sweeps through an av… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.07586v3-abstract-full').style.display = 'inline'; document.getElementById('2103.07586v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2103.07586v3-abstract-full" style="display: none;"> Landau-Zener physics is often exploited to generate quantum logic gates and to perform state initialization and readout. The quality of these operations can be degraded by noise fluctuations in the energy gap at the avoided crossing. We leverage a recently discovered correspondence between qubit evolution and space curves in three dimensions to design noise-robust Landau-Zener sweeps through an avoided crossing. In the case where the avoided crossing is purely noise-induced, we prove that operations based on monotonic sweeps cannot be robust to noise. Hence, we design families of phase gates based on non-monotonic drives that are error-robust up to second order. In the general case where there is an avoided crossing even in the absence of noise, we present a general technique for designing robust driving protocols that takes advantage of a relationship between the Landau-Zener problem and space curves of constant torsion. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2103.07586v3-abstract-full').style.display = 'none'; document.getElementById('2103.07586v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 31 January, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 12 March, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages, 11 figures; v3: final published version</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Quantum 6, 639 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2101.11592">arXiv:2101.11592</a> <span> [<a href="https://arxiv.org/pdf/2101.11592">pdf</a>, <a href="https://arxiv.org/format/2101.11592">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Mesoscale and Nanoscale Physics">cond-mat.mes-hall</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevB.106.165302">10.1103/PhysRevB.106.165302 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Fast high-fidelity single-qubit gates for flip-flop qubits in silicon </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Calderon-Vargas%2C+F+A">Fernando A. Calderon-Vargas</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2101.11592v2-abstract-short" style="display: inline;"> The flip-flop qubit, encoded in the states with antiparallel donor-bound electron and donor nuclear spins in silicon, showcases long coherence times, good controllability, and, in contrast to other donor-spin-based schemes, long-distance coupling. Electron spin control near the interface, however, is likely to shorten the relaxation time by many orders of magnitude, reducing the overall qubit qual… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.11592v2-abstract-full').style.display = 'inline'; document.getElementById('2101.11592v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2101.11592v2-abstract-full" style="display: none;"> The flip-flop qubit, encoded in the states with antiparallel donor-bound electron and donor nuclear spins in silicon, showcases long coherence times, good controllability, and, in contrast to other donor-spin-based schemes, long-distance coupling. Electron spin control near the interface, however, is likely to shorten the relaxation time by many orders of magnitude, reducing the overall qubit quality factor. Here, we theoretically study the multilevel system that is formed by the interacting electron and nuclear spins and derive analytical effective two-level Hamiltonians with and without periodic driving. We then propose an optimal control scheme that produces fast and robust single-qubit gates in the presence of low-frequency noise without relying on parametrically restrictive sweet spots. This scheme increases considerably both the relaxation time and the qubit quality factor. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.11592v2-abstract-full').style.display = 'none'; document.getElementById('2101.11592v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 October, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 27 January, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Published version, 16 pages, 8 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. B 106, 165302 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2101.11579">arXiv:2101.11579</a> <span> [<a href="https://arxiv.org/pdf/2101.11579">pdf</a>, <a href="https://arxiv.org/format/2101.11579">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevB.104.115308">10.1103/PhysRevB.104.115308 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Robust photon-mediated entangling gates between quantum dot spin qubits </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Warren%2C+A">Ada Warren</a>, <a href="/search/quant-ph?searchtype=author&query=G%C3%BCng%C3%B6rd%C3%BC%2C+U">Utkan G眉ng枚rd眉</a>, <a href="/search/quant-ph?searchtype=author&query=Kestner%2C+J+P">J. P. Kestner</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2101.11579v1-abstract-short" style="display: inline;"> Significant experimental advances in single-electron silicon spin qubits have opened the possibility of realizing long-range entangling gates mediated by microwave photons. Recently proposed iSWAP gates, however, require tuning qubit energies into resonance and have limited fidelity due to charge noise. We present a novel photon-mediated cross-resonance gate that is consistent with realistic exper… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.11579v1-abstract-full').style.display = 'inline'; document.getElementById('2101.11579v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2101.11579v1-abstract-full" style="display: none;"> Significant experimental advances in single-electron silicon spin qubits have opened the possibility of realizing long-range entangling gates mediated by microwave photons. Recently proposed iSWAP gates, however, require tuning qubit energies into resonance and have limited fidelity due to charge noise. We present a novel photon-mediated cross-resonance gate that is consistent with realistic experimental capabilities and requires no resonant tuning. Furthermore, we propose gate sequences capable of suppressing errors due to quasistatic noise for both the cross-resonance and iSWAP gates. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.11579v1-abstract-full').style.display = 'none'; document.getElementById('2101.11579v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 27 January, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, 4 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. B 104, 115308 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2101.11082">arXiv:2101.11082</a> <span> [<a href="https://arxiv.org/pdf/2101.11082">pdf</a>, <a href="https://arxiv.org/format/2101.11082">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevA.104.052623">10.1103/PhysRevA.104.052623 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Error-correcting entanglement swapping using a practical logical photon encoding </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Hilaire%2C+P">Paul Hilaire</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Grosshans%2C+F">Fr茅d茅ric Grosshans</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2101.11082v4-abstract-short" style="display: inline;"> Several emerging quantum technologies, including quantum networks, modular and fusion-based quantum computing, rely crucially on the ability to perform photonic Bell state measurements. Therefore, photon losses and the 50\% success probablity upper bound of Bell state measurements pose a critical limitation to photonic quantum technologies. Here, we develop protocols that overcome these two key ch… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.11082v4-abstract-full').style.display = 'inline'; document.getElementById('2101.11082v4-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2101.11082v4-abstract-full" style="display: none;"> Several emerging quantum technologies, including quantum networks, modular and fusion-based quantum computing, rely crucially on the ability to perform photonic Bell state measurements. Therefore, photon losses and the 50\% success probablity upper bound of Bell state measurements pose a critical limitation to photonic quantum technologies. Here, we develop protocols that overcome these two key challenges through logical encoding of photonic qubits. Our approach uses a tree graph state logical encoding, which can be produced deterministically with a few quantum emitters, and achieves near-deterministic logical photonic Bell state measurements while also protecting against errors including photon losses, with a record loss-tolerance threshold. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.11082v4-abstract-full').style.display = 'none'; document.getElementById('2101.11082v4-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 September, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 26 January, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages, 5 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2012.07227">arXiv:2012.07227</a> <span> [<a href="https://arxiv.org/pdf/2012.07227">pdf</a>, <a href="https://arxiv.org/format/2012.07227">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Mesoscale and Nanoscale Physics">cond-mat.mes-hall</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevB.103.235301">10.1103/PhysRevB.103.235301 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Driven dynamics of a quantum dot electron spin coupled to bath of higher-spin nuclei </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Vezvaee%2C+A">Arian Vezvaee</a>, <a href="/search/quant-ph?searchtype=author&query=Sharma%2C+G">Gargee Sharma</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2012.07227v2-abstract-short" style="display: inline;"> The interplay of optical driving and hyperfine interaction between an electron confined in a quantum dot and its surrounding nuclear spin environment produces a range of interesting physics such as mode-locking. In this work, we go beyond the ubiquitous spin 1/2 approximation for nuclear spins and present a comprehensive theoretical framework for an optically driven electron spin in a self-assem… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.07227v2-abstract-full').style.display = 'inline'; document.getElementById('2012.07227v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2012.07227v2-abstract-full" style="display: none;"> The interplay of optical driving and hyperfine interaction between an electron confined in a quantum dot and its surrounding nuclear spin environment produces a range of interesting physics such as mode-locking. In this work, we go beyond the ubiquitous spin 1/2 approximation for nuclear spins and present a comprehensive theoretical framework for an optically driven electron spin in a self-assembled quantum dot coupled to a nuclear spin bath of arbitrary spin. Using a dynamical mean-field approach, we compute the nuclear spin polarization distribution with and without the quadrupolar coupling. We find that while hyperfine interactions drive dynamic nuclear polarization and mode-locking, quadrupolar couplings counteract these effects. The tension between these mechanisms is imprinted on the steady-state electron spin evolution, providing a way to measure the importance of quadrupolar interactions in a quantum dot. Our results show that higher-spin effects such as quadrupolar interactions can have a significant impact on the generation of dynamic nuclear polarization and how it influences the electron spin evolution. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.07227v2-abstract-full').style.display = 'none'; document.getElementById('2012.07227v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 17 December, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 13 December, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. B 103, 235301 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2009.08469">arXiv:2009.08469</a> <span> [<a href="https://arxiv.org/pdf/2009.08469">pdf</a>, <a href="https://arxiv.org/format/2009.08469">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Mesoscale and Nanoscale Physics">cond-mat.mes-hall</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevB.103.245303">10.1103/PhysRevB.103.245303 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Protecting Quantum Information in Quantum Dot Spin Chains by Driving Exchange Interactions Periodically </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Van+Dyke%2C+J+S">John S. Van Dyke</a>, <a href="/search/quant-ph?searchtype=author&query=Kandel%2C+Y+P">Yadav P. Kandel</a>, <a href="/search/quant-ph?searchtype=author&query=Qiao%2C+H">Haifeng Qiao</a>, <a href="/search/quant-ph?searchtype=author&query=Nichol%2C+J+M">John M. Nichol</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2009.08469v1-abstract-short" style="display: inline;"> Recent work has demonstrated a new route to discrete time crystal physics in quantum spin chains by periodically driving nearest-neighbor exchange interactions in gate-defined quantum dot arrays [arXiv:2006.10913]. Here, we present a detailed analysis of exchange-driven Floquet physics in small arrays of GaAs quantum dots, including phase diagrams and additional diagnostics. We also show that emer… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.08469v1-abstract-full').style.display = 'inline'; document.getElementById('2009.08469v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2009.08469v1-abstract-full" style="display: none;"> Recent work has demonstrated a new route to discrete time crystal physics in quantum spin chains by periodically driving nearest-neighbor exchange interactions in gate-defined quantum dot arrays [arXiv:2006.10913]. Here, we present a detailed analysis of exchange-driven Floquet physics in small arrays of GaAs quantum dots, including phase diagrams and additional diagnostics. We also show that emergent time-crystalline behavior can benefit the protection and manipulation of multi-spin states. For typical levels of nuclear spin noise in GaAs, the combination of driving and interactions protects spin-singlet states beyond what is possible in the absence of exchange interactions. We further show how to construct a time-crystal-inspired CZ gate between singlet-triplet qubits with high fidelity. These results show that periodically driving exchange couplings can enhance the performance of quantum dot spin systems for quantum information applications. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.08469v1-abstract-full').style.display = 'none'; document.getElementById('2009.08469v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 17 September, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 16 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. B 103, 245303 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2008.04302">arXiv:2008.04302</a> <span> [<a href="https://arxiv.org/pdf/2008.04302">pdf</a>, <a href="https://arxiv.org/format/2008.04302">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Strongly Correlated Electrons">cond-mat.str-el</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Chemical Physics">physics.chem-ph</span> </div> </div> <p class="title is-5 mathjax"> Gate-free state preparation for fast variational quantum eigensolver simulations: ctrl-VQE </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Meitei%2C+O+R">Oinam Romesh Meitei</a>, <a href="/search/quant-ph?searchtype=author&query=Gard%2C+B+T">Bryan T. Gard</a>, <a href="/search/quant-ph?searchtype=author&query=Barron%2C+G+S">George S. Barron</a>, <a href="/search/quant-ph?searchtype=author&query=Pappas%2C+D+P">David P. Pappas</a>, <a href="/search/quant-ph?searchtype=author&query=Economou%2C+S+E">Sophia E. Economou</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a>, <a href="/search/quant-ph?searchtype=author&query=Mayhall%2C+N+J">Nicholas J. Mayhall</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2008.04302v3-abstract-short" style="display: inline;"> The variational quantum eigensolver (VQE) is currently the flagship algorithm for solving electronic structure problems on near-term quantum computers. This hybrid quantum/classical algorithm involves implementing a sequence of parameterized gates on quantum hardware to generate a target quantum state, and then measuring the expectation value of the molecular Hamiltonian. Due to finite coherence t… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.04302v3-abstract-full').style.display = 'inline'; document.getElementById('2008.04302v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2008.04302v3-abstract-full" style="display: none;"> The variational quantum eigensolver (VQE) is currently the flagship algorithm for solving electronic structure problems on near-term quantum computers. This hybrid quantum/classical algorithm involves implementing a sequence of parameterized gates on quantum hardware to generate a target quantum state, and then measuring the expectation value of the molecular Hamiltonian. Due to finite coherence times and frequent gate errors, the number of gates that can be implemented remains limited on current quantum devices, preventing accurate applications to systems with significant entanglement, such as strongly correlated molecules. In this work, we propose an alternative algorithm (which we refer to as ctrl-VQE) where the quantum circuit used for state preparation is removed entirely and replaced by a quantum control routine which variationally shapes a pulse to drive the initial Hartree-Fock state to the full CI target state. As with VQE, the objective function optimized is the expectation value of the qubit-mapped molecular Hamiltonian. However, by removing the quantum circuit, the coherence times required for state preparation can be drastically reduced by directly optimizing the pulses. We demonstrate the potential of this method numerically by directly optimizing pulse shapes which accurately model the dissociation curves of the hydrogen molecule (covalent bond) and helium hydride ion (ionic bond), and we compute the single point energy for LiH with four transmons. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.04302v3-abstract-full').style.display = 'none'; document.getElementById('2008.04302v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 May, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 10 August, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2020. </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2008.01168">arXiv:2008.01168</a> <span> [<a href="https://arxiv.org/pdf/2008.01168">pdf</a>, <a href="https://arxiv.org/format/2008.01168">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="Quantum Physics">quant-ph</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PRXQuantum.2.010341">10.1103/PRXQuantum.2.010341 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Geometrical Formalism for Dynamically Corrected Gates in Multiqubit Systems </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/quant-ph?searchtype=author&query=Buterakos%2C+D">Donovan Buterakos</a>, <a href="/search/quant-ph?searchtype=author&query=Sarma%2C+S+D">Sankar Das Sarma</a>, <a href="/search/quant-ph?searchtype=author&query=Barnes%2C+E">Edwin Barnes</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2008.01168v1-abstract-short" style="display: inline;"> The ability to perform gates in multiqubit systems that are robust to noise is of crucial importance for the advancement of quantum information technologies. However, finding control pulses that cancel noise while performing a gate is made difficult by the intractability of the time-dependent Schrodinger equation, especially in multiqubit systems. Here, we show that this issue can be sidestepped b… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.01168v1-abstract-full').style.display = 'inline'; document.getElementById('2008.01168v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2008.01168v1-abstract-full" style="display: none;"> The ability to perform gates in multiqubit systems that are robust to noise is of crucial importance for the advancement of quantum information technologies. However, finding control pulses that cancel noise while performing a gate is made difficult by the intractability of the time-dependent Schrodinger equation, especially in multiqubit systems. Here, we show that this issue can be sidestepped by using a formalism in which the cumulative error during a gate is represented geometrically as a curve in a multi-dimensional Euclidean space. Cancellation of noise errors to leading order corresponds to closure of the curve, a condition that can be satisfied without solving the Schrodinger equation. We develop and uncover general properties of this geometric formalism, and derive a recursion relation that maps control fields to curvatures for Hamiltonians of arbitrary dimension. We demonstrate examples by using the geometric method to design dynamically corrected gates for a class of two-qubit Hamiltonians that is relevant for both superconducting transmon qubits and semiconductor spin qubits. We propose this geometric formalism as a general technique for pulse-induced error suppression in quantum computing gate operations. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.01168v1-abstract-full').style.display = 'none'; document.getElementById('2008.01168v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 July, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, 4 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> PRX Quantum 2, 010341 (2021) </p> </li> </ol> <nav class="pagination is-small is-centered breathe-horizontal" 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