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</div> <div class="control"> <button class="button is-small is-link">Go</button> </div> </div> </form> </div> </div> <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/2502.01040">arXiv:2502.01040</a> <span> [<a href="https://arxiv.org/pdf/2502.01040">pdf</a>, <a href="https://arxiv.org/format/2502.01040">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> </div> </div> <p class="title is-5 mathjax"> Enhancement of Electric Drive in Silicon Quantum Dots with Electric Quadrupole Spin Resonance </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Mai%2C+P+Y">Philip Y. Mai</a>, <a href="/search/cond-mat?searchtype=author&query=Pereira%2C+P+H">Pedro H. Pereira</a>, <a href="/search/cond-mat?searchtype=author&query=Alonso%2C+L+A">Lucas Andrade Alonso</a>, <a href="/search/cond-mat?searchtype=author&query=Leon%2C+R+C+C">Ross C. C. Leon</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">Chih Hwan Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">Jason C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Dunmore%2C+D">Daniel Dunmore</a>, <a href="/search/cond-mat?searchtype=author&query=Lemyre%2C+J+C">Julien Camirand Lemyre</a>, <a href="/search/cond-mat?searchtype=author&query=Tanttu%2C+T">Tuomo Tanttu</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">Wister Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Chan%2C+K+W">Kok Wai Chan</a>, <a href="/search/cond-mat?searchtype=author&query=Tan%2C+K+Y">Kuan Yen Tan</a>, <a href="/search/cond-mat?searchtype=author&query=Cifuentes%2C+J+D">Jes煤s D. Cifuentes</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">Fay E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">Kohei M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">Arne Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Pioro-Ladri%C3%A8re%2C+M">Michel Pioro-Ladri猫re</a>, <a href="/search/cond-mat?searchtype=author&query=Escott%2C+C+C">Christopher C. Escott</a>, <a href="/search/cond-mat?searchtype=author&query=Feng%2C+M">MengKe Feng</a>, <a href="/search/cond-mat?searchtype=author&query=Souza%2C+R+d+M+e">Reinaldo de Melo e Souza</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A">Andrew Dzurak</a>, <a href="/search/cond-mat?searchtype=author&query=Saraiva%2C+A">Andre Saraiva</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="2502.01040v2-abstract-short" style="display: inline;"> Quantum computation with electron spin qubits requires coherent and efficient manipulation of these spins, typically accomplished through the application of alternating magnetic or electric fields for electron spin resonance (ESR). In particular, electrical driving allows us to apply localized fields on the electrons, which benefits scale-up architectures. However, we have found that Electric Dipo… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2502.01040v2-abstract-full').style.display = 'inline'; document.getElementById('2502.01040v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2502.01040v2-abstract-full" style="display: none;"> Quantum computation with electron spin qubits requires coherent and efficient manipulation of these spins, typically accomplished through the application of alternating magnetic or electric fields for electron spin resonance (ESR). In particular, electrical driving allows us to apply localized fields on the electrons, which benefits scale-up architectures. However, we have found that Electric Dipole Spin Resonance (EDSR) is insufficient for modeling the Rabi behavior in recent experimental studies. Therefore, we propose that the electron spin is being driven by a new method of electric spin qubit control which generalizes the spin dynamics by taking into account a quadrupolar contribution of the quantum dot: electric quadrupole spin resonance (EQSR). In this work, we explore the electric quadrupole driving of a quantum dot in silicon, specifically examining the cases of 5 and 13 electron occupancies. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2502.01040v2-abstract-full').style.display = 'none'; document.getElementById('2502.01040v2-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 February, 2025; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 2 February, 2025; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2025. </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">Main: 5 pages, 4 figures Supp: 4 pages</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2008.03968">arXiv:2008.03968</a> <span> [<a href="https://arxiv.org/pdf/2008.03968">pdf</a>, <a href="https://arxiv.org/format/2008.03968">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> </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/s41467-021-23437-w">10.1038/s41467-021-23437-w <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Bell-state tomography in a silicon many-electron artificial molecule </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Leon%2C+R+C+C">Ross C. C. Leon</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">Chih Hwan Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">Jason C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Lemyre%2C+J+C">Julien Camirand Lemyre</a>, <a href="/search/cond-mat?searchtype=author&query=Tanttu%2C+T">Tuomo Tanttu</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">Wei Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+J+Y">Jonathan Y. Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">Fay E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">Kohei M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">Arne Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Pioro-Ladri%C3%A8re%2C+M">Michel Pioro-Ladri猫re</a>, <a href="/search/cond-mat?searchtype=author&query=Saraiva%2C+A">Andre Saraiva</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">Andrew S. Dzurak</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="2008.03968v1-abstract-short" style="display: inline;"> An error-corrected quantum processor will require millions of qubits, accentuating the advantage of nanoscale devices with small footprints, such as silicon quantum dots. However, as for every device with nanoscale dimensions, disorder at the atomic level is detrimental to qubit uniformity. Here we investigate two spin qubits confined in a silicon double-quantum-dot artificial molecule. Each quant… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.03968v1-abstract-full').style.display = 'inline'; document.getElementById('2008.03968v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2008.03968v1-abstract-full" style="display: none;"> An error-corrected quantum processor will require millions of qubits, accentuating the advantage of nanoscale devices with small footprints, such as silicon quantum dots. However, as for every device with nanoscale dimensions, disorder at the atomic level is detrimental to qubit uniformity. Here we investigate two spin qubits confined in a silicon double-quantum-dot artificial molecule. Each quantum dot has a robust shell structure and, when operated at an occupancy of 5 or 13 electrons, has single spin-$\frac{1}{2}$ valence electron in its $p$- or $d$-orbital, respectively. These higher electron occupancies screen atomic-level disorder. The larger multielectron wavefunctions also enable significant overlap between neighbouring qubit electrons, while making space for an interstitial exchange-gate electrode. We implement a universal gate set using the magnetic field gradient of a micromagnet for electrically-driven single qubit gates, and a gate-voltage-controlled inter-dot barrier to perform two-qubit gates by pulsed exchange coupling. We use this gate set to demonstrate a Bell state preparation between multielectron qubits with fidelity 90.3%, confirmed by two-qubit state tomography using spin parity measurements. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.03968v1-abstract-full').style.display = 'none'; document.getElementById('2008.03968v1-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 August, 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">Journal ref:</span> Nature Communications 12, 3228 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2004.07666">arXiv:2004.07666</a> <span> [<a href="https://arxiv.org/pdf/2004.07666">pdf</a>, <a href="https://arxiv.org/format/2004.07666">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/10.1021/acs.nanolett.0c04771">10.1021/acs.nanolett.0c04771 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Exchange coupling in a linear chain of three quantum-dot spin qubits in silicon </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Chan%2C+K+W">Kok Wai Chan</a>, <a href="/search/cond-mat?searchtype=author&query=Sahasrabudhe%2C+H">Harshad Sahasrabudhe</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">Wister Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Wang%2C+Y">Yu Wang</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+H+C">Henry C. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Veldhorst%2C+M">Menno Veldhorst</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">Jason C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Mohiyaddin%2C+F+A">Fahd A. Mohiyaddin</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">Fay E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">Kohei M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Saraiva%2C+A">Andre Saraiva</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">Andrea Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">Arne Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Rahman%2C+R">Rajib Rahman</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">Andrew S. Dzurak</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="2004.07666v1-abstract-short" style="display: inline;"> Quantum gates between spin qubits can be implemented leveraging the natural Heisenberg exchange interaction between two electrons in contact with each other. This interaction is controllable by electrically tailoring the overlap between electronic wavefunctions in quantum dot systems, as long as they occupy neighbouring dots. An alternative route is the exploration of superexchange - the coupling… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.07666v1-abstract-full').style.display = 'inline'; document.getElementById('2004.07666v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2004.07666v1-abstract-full" style="display: none;"> Quantum gates between spin qubits can be implemented leveraging the natural Heisenberg exchange interaction between two electrons in contact with each other. This interaction is controllable by electrically tailoring the overlap between electronic wavefunctions in quantum dot systems, as long as they occupy neighbouring dots. An alternative route is the exploration of superexchange - the coupling between remote spins mediated by a third idle electron that bridges the distance between quantum dots. We experimentally demonstrate direct exchange coupling and provide evidence for second neighbour mediated superexchange in a linear array of three single-electron spin qubits in silicon, inferred from the electron spin resonance frequency spectra. We confirm theoretically through atomistic modeling that the device geometry only allows for sizeable direct exchange coupling for neighbouring dots, while next nearest neighbour coupling cannot stem from the vanishingly small tail of the electronic wavefunction of the remote dots, and is only possible if mediated. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.07666v1-abstract-full').style.display = 'none'; document.getElementById('2004.07666v1-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 April, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 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">20 pages, 1.4MB, 4 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nano Letters 2021, 21, 3, 1517-1522 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1902.09126">arXiv:1902.09126</a> <span> [<a href="https://arxiv.org/pdf/1902.09126">pdf</a>, <a href="https://arxiv.org/format/1902.09126">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/10.1038/s41586-020-2171-6">10.1038/s41586-020-2171-6 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Silicon quantum processor unit cell operation above one Kelvin </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Leon%2C+R+C+C">R. C. C. Leon</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Saraiva%2C+A">A. Saraiva</a>, <a href="/search/cond-mat?searchtype=author&query=Tanttu%2C+T">T. Tanttu</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">W. Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Lemyre%2C+J+C">J. Camirand Lemyre</a>, <a href="/search/cond-mat?searchtype=author&query=Chan%2C+K+W">K. W. Chan</a>, <a href="/search/cond-mat?searchtype=author&query=Tan%2C+K+Y">K. Y. Tan</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Pioro-Ladri%C3%A8re%2C+M">M. Pioro-Ladri猫re</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">A. Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1902.09126v2-abstract-short" style="display: inline;"> Quantum computers are expected to outperform conventional computers for a range of important problems, from molecular simulation to search algorithms, once they can be scaled up to large numbers of quantum bits (qubits), typically millions. For most solid-state qubit technologies, e.g. those using superconducting circuits or semiconductor spins, scaling poses a significant challenge as every addit… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1902.09126v2-abstract-full').style.display = 'inline'; document.getElementById('1902.09126v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1902.09126v2-abstract-full" style="display: none;"> Quantum computers are expected to outperform conventional computers for a range of important problems, from molecular simulation to search algorithms, once they can be scaled up to large numbers of quantum bits (qubits), typically millions. For most solid-state qubit technologies, e.g. those using superconducting circuits or semiconductor spins, scaling poses a significant challenge as every additional qubit increases the heat generated, while the cooling power of dilution refrigerators is severely limited at their operating temperature below 100 mK. Here we demonstrate operation of a scalable silicon quantum processor unit cell, comprising two qubits confined to quantum dots (QDs) at $\sim$1.5 Kelvin. We achieve this by isolating the QDs from the electron reservoir, initialising and reading the qubits solely via tunnelling of electrons between the two QDs. We coherently control the qubits using electrically-driven spin resonance (EDSR) in isotopically enriched silicon $^{28}$Si, attaining single-qubit gate fidelities of 98.6% and coherence time $T_2^*$ = 2$渭$s during `hot' operation, comparable to those of spin qubits in natural silicon at millikelvin temperatures. Furthermore, we show that the unit cell can be operated at magnetic fields as low as 0.1 T, corresponding to a qubit control frequency of 3.5 GHz, where the qubit energy is well below the thermal energy. The unit cell constitutes the core building block of a full-scale silicon quantum computer, and satisfies layout constraints required by error correction architectures. Our work indicates that a spin-based quantum computer could be operated at elevated temperatures in a simple pumped $^4$He system, offering orders of magnitude higher cooling power than dilution refrigerators, potentially enabling classical control electronics to be integrated with the qubit array. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1902.09126v2-abstract-full').style.display = 'none'; document.getElementById('1902.09126v2-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> 19 June, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 25 February, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nature 580, 350-354 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1902.01550">arXiv:1902.01550</a> <span> [<a href="https://arxiv.org/pdf/1902.01550">pdf</a>, <a href="https://arxiv.org/format/1902.01550">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> </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/s41467-019-14053-w">10.1038/s41467-019-14053-w <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Coherent spin control of s-, p-, d- and f-electrons in a silicon quantum dot </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Leon%2C+R+C+C">R. C. C. Leon</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Lemyre%2C+J+C">J. Camirand Lemyre</a>, <a href="/search/cond-mat?searchtype=author&query=Tanttu%2C+T">T. Tanttu</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">W. Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Chan%2C+K+W">K. W. Chan</a>, <a href="/search/cond-mat?searchtype=author&query=Tan%2C+K+Y">K. Y. Tan</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">A. Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Pioro-Ladriere%2C+M">M. Pioro-Ladriere</a>, <a href="/search/cond-mat?searchtype=author&query=Saraiva%2C+A">A. Saraiva</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1902.01550v3-abstract-short" style="display: inline;"> Once the periodic properties of elements were unveiled, chemical bonds could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots, often termed artificial atoms, and quantum computation could be performed by merely controlling the outer-shell electrons of dot-based qubits. Imperfections in the semiconductor material, including at the atomic scale, di… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1902.01550v3-abstract-full').style.display = 'inline'; document.getElementById('1902.01550v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1902.01550v3-abstract-full" style="display: none;"> Once the periodic properties of elements were unveiled, chemical bonds could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots, often termed artificial atoms, and quantum computation could be performed by merely controlling the outer-shell electrons of dot-based qubits. Imperfections in the semiconductor material, including at the atomic scale, disrupt this analogy between atoms and quantum dots, so that real devices seldom display such a systematic many-electron arrangement. We demonstrate here an electrostatically-defined quantum dot that is robust to disorder, revealing a well defined shell structure. We observe four shells (31 electrons) with multiplicities given by spin and valley degrees of freedom. We explore various fillings consisting of a single valence electron -- namely 1, 5, 13 and 25 electrons -- as potential qubits, and we identify fillings that yield a total spin-1 on the dot. An integrated micromagnet allows us to perform electrically-driven spin resonance (EDSR). Higher shell states are shown to be more susceptible to the driving field, leading to faster Rabi rotations of the qubit. We investigate the impact of orbital excitations of the p- and d-shell electrons on single qubits as a function of the dot deformation. This allows us to tune the dot excitation spectrum and exploit it for faster qubit control. Furthermore, hotspots arising from this tunable energy level structure provide a pathway towards fast spin initialisation. The observation of spin-1 states may be exploited in the future to study symmetry-protected topological states in antiferromagnetic spin chains and their application to quantum computing. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1902.01550v3-abstract-full').style.display = 'none'; document.getElementById('1902.01550v3-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 May, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 5 February, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nature Communications 11, 797 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1812.08347">arXiv:1812.08347</a> <span> [<a href="https://arxiv.org/pdf/1812.08347">pdf</a>, <a href="https://arxiv.org/format/1812.08347">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> </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/s41467-019-13416-7">10.1038/s41467-019-13416-7 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Single-spin qubits in isotopically enriched silicon at low magnetic field </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Zhao%2C+R">R. Zhao</a>, <a href="/search/cond-mat?searchtype=author&query=Tanttu%2C+T">T. Tanttu</a>, <a href="/search/cond-mat?searchtype=author&query=Tan%2C+K+Y">K. Y. Tan</a>, <a href="/search/cond-mat?searchtype=author&query=Hensen%2C+B">B. Hensen</a>, <a href="/search/cond-mat?searchtype=author&query=Chan%2C+K+W">K. W. Chan</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Leon%2C+R+C+C">R. C. C. Leon</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Gilbert%2C+W">W. Gilbert</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Kiselev%2C+A+A">A. A. Kiselev</a>, <a href="/search/cond-mat?searchtype=author&query=Ladd%2C+T+D">T. D. Ladd</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">A. Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1812.08347v5-abstract-short" style="display: inline;"> Single-electron spin qubits employ magnetic fields on the order of 1 Tesla or above to enable quantum state readout via spin-dependent-tunnelling. This requires demanding microwave engineering for coherent spin resonance control and significant on-chip real estate for electron reservoirs, both of which limit the prospects for large scale multi-qubit systems. Alternatively, singlet-triplet (ST) rea… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1812.08347v5-abstract-full').style.display = 'inline'; document.getElementById('1812.08347v5-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1812.08347v5-abstract-full" style="display: none;"> Single-electron spin qubits employ magnetic fields on the order of 1 Tesla or above to enable quantum state readout via spin-dependent-tunnelling. This requires demanding microwave engineering for coherent spin resonance control and significant on-chip real estate for electron reservoirs, both of which limit the prospects for large scale multi-qubit systems. Alternatively, singlet-triplet (ST) readout enables high-fidelity spin-state measurements in much lower magnetic fields, without the need for reservoirs. Here, we demonstrate low-field operation of metal-oxide-silicon (MOS) quantum dot qubits by combining coherent single-spin control with high-fidelity, single-shot, Pauli-spin-blockade-based ST readout. We discover that the qubits decohere faster at low magnetic fields with $T_{2}^{Rabi}=18.6$~$渭$s and $T_2^*=1.4$~$渭$s at 150~mT. Their coherence is limited by spin flips of residual $^{29}$Si nuclei in the isotopically enriched $^{28}$Si host material, which occur more frequently at lower fields. Our finding indicates that new trade-offs will be required to ensure the frequency stabilization of spin qubits and highlights the importance of isotopic enrichment of device substrates for the realization of a scalable silicon-based quantum processor. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1812.08347v5-abstract-full').style.display = 'none'; document.getElementById('1812.08347v5-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 August, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 19 December, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nat Commun 10, 5500 (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1807.09500">arXiv:1807.09500</a> <span> [<a href="https://arxiv.org/pdf/1807.09500">pdf</a>, <a href="https://arxiv.org/format/1807.09500">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/10.1038/s41928-019-0234-1">10.1038/s41928-019-0234-1 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Silicon qubit fidelities approaching incoherent noise limits via pulse engineering </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Chan%2C+K+W">K. W. Chan</a>, <a href="/search/cond-mat?searchtype=author&query=Harper%2C+R">R. Harper</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">W. Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Evans%2C+T">T. Evans</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Hensen%2C+B">B. Hensen</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">A. Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Tanttu%2C+T">T. Tanttu</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Flammia%2C+S+T">S. T. Flammia</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Bartlett%2C+S+D">S. D. Bartlett</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1807.09500v3-abstract-short" style="display: inline;"> The performance requirements for fault-tolerant quantum computing are very stringent. Qubits must be manipulated, coupled, and measured with error rates well below 1%. For semiconductor implementations, silicon quantum dot spin qubits have demonstrated average single-qubit Clifford gate error rates that approach this threshold, notably with error rates of 0.14% in isotopically enriched $^{28}$Si/S… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1807.09500v3-abstract-full').style.display = 'inline'; document.getElementById('1807.09500v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1807.09500v3-abstract-full" style="display: none;"> The performance requirements for fault-tolerant quantum computing are very stringent. Qubits must be manipulated, coupled, and measured with error rates well below 1%. For semiconductor implementations, silicon quantum dot spin qubits have demonstrated average single-qubit Clifford gate error rates that approach this threshold, notably with error rates of 0.14% in isotopically enriched $^{28}$Si/SiGe devices. This gate performance, together with high-fidelity two-qubit gates and measurements, is only known to meet the threshold for fault-tolerant quantum computing in some architectures when assuming that the noise is incoherent, and still lower error rates are needed to reduce overhead. Here we experimentally show that pulse engineering techniques, widely used in magnetic resonance, improve average Clifford gate error rates for silicon quantum dot spin qubits to 0.043%,a factor of 3 improvement on previous best results for silicon quantum dot devices. By including tomographically complete measurements in randomised benchmarking, we infer a higher-order feature of the noise called the unitarity, which measures the coherence of noise. This in turn allows us to theoretically predict that average gate error rates as low as 0.026% may be achievable with further pulse improvements. These fidelities are ultimately limited by Markovian noise, which we attribute to charge noise emanating from the silicon device structure itself, or the environment. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1807.09500v3-abstract-full').style.display = 'none'; document.getElementById('1807.09500v3-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, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 25 July, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nature Electronics 2, 151-158 (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1805.05027">arXiv:1805.05027</a> <span> [<a href="https://arxiv.org/pdf/1805.05027">pdf</a>, <a href="https://arxiv.org/format/1805.05027">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/10.1038/s41586-019-1197-0">10.1038/s41586-019-1197-0 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Fidelity benchmarks for two-qubit gates in silicon </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">W. Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Chan%2C+K+W">K. W. Chan</a>, <a href="/search/cond-mat?searchtype=author&query=Tanttu%2C+T">T. Tanttu</a>, <a href="/search/cond-mat?searchtype=author&query=Hensen%2C+B">B. Hensen</a>, <a href="/search/cond-mat?searchtype=author&query=Leon%2C+R+C+C">R. C. C. Leon</a>, <a href="/search/cond-mat?searchtype=author&query=Fogarty%2C+M+A">M. A. Fogarty</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">A. Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1805.05027v3-abstract-short" style="display: inline;"> Universal quantum computation will require qubit technology based on a scalable platform, together with quantum error correction protocols that place strict limits on the maximum infidelities for one- and two-qubit gate operations. While a variety of qubit systems have shown high fidelities at the one-qubit level, superconductor technologies have been the only solid-state qubits manufactured via s… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1805.05027v3-abstract-full').style.display = 'inline'; document.getElementById('1805.05027v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1805.05027v3-abstract-full" style="display: none;"> Universal quantum computation will require qubit technology based on a scalable platform, together with quantum error correction protocols that place strict limits on the maximum infidelities for one- and two-qubit gate operations. While a variety of qubit systems have shown high fidelities at the one-qubit level, superconductor technologies have been the only solid-state qubits manufactured via standard lithographic techniques which have demonstrated two-qubit fidelities near the fault-tolerant threshold. Silicon-based quantum dot qubits are also amenable to large-scale manufacture and can achieve high single-qubit gate fidelities (exceeding 99.9%) using isotopically enriched silicon. However, while two-qubit gates have been demonstrated in silicon, it has not yet been possible to rigorously assess their fidelities using randomized benchmarking, since this requires sequences of significant numbers of qubit operations ($\gtrsim 20$) to be completed with non-vanishing fidelity. Here, for qubits encoded on the electron spin states of gate-defined quantum dots, we demonstrate Bell state tomography with fidelities ranging from 80% to 89%, and two-qubit randomized benchmarking with an average Clifford gate fidelity of 94.7% and average Controlled-ROT (CROT) fidelity of 98.0%. These fidelities are found to be limited by the relatively slow gate times employed here compared with the decoherence times $T_2^*$ of the qubits. Silicon qubit designs employing fast gate operations based on high Rabi frequencies, together with advanced pulsing techniques, should therefore enable significantly higher fidelities in the near future. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1805.05027v3-abstract-full').style.display = 'none'; document.getElementById('1805.05027v3-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 July, 2018; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 14 May, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nature 569, 532-536 (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1608.07748">arXiv:1608.07748</a> <span> [<a href="https://arxiv.org/pdf/1608.07748">pdf</a>, <a href="https://arxiv.org/format/1608.07748">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> </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.96.045302">10.1103/PhysRevB.96.045302 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Impact of g-factors and valleys on spin qubits in a silicon double quantum dot </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Veldhorst%2C+M">M. Veldhorst</a>, <a href="/search/cond-mat?searchtype=author&query=Hendrickx%2C+N">N. Hendrickx</a>, <a href="/search/cond-mat?searchtype=author&query=Fogarty%2C+M+A">M. A. Fogarty</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">W. Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1608.07748v2-abstract-short" style="display: inline;"> We define single electron spin qubits in a silicon MOS double quantum dot system. By mapping the qubit resonance frequency as a function of gate-induced electric field, the spectrum reveals an anticrossing that is consistent with an inter-valley spin-orbit coupling. We fit the data from which we extract an inter-valley coupling strength of 43 MHz. In addition, we observe a narrow resonance near th… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1608.07748v2-abstract-full').style.display = 'inline'; document.getElementById('1608.07748v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1608.07748v2-abstract-full" style="display: none;"> We define single electron spin qubits in a silicon MOS double quantum dot system. By mapping the qubit resonance frequency as a function of gate-induced electric field, the spectrum reveals an anticrossing that is consistent with an inter-valley spin-orbit coupling. We fit the data from which we extract an inter-valley coupling strength of 43 MHz. In addition, we observe a narrow resonance near the primary qubit resonance when we operate the device in the (1,1) charge configuration. The experimental data is consistent with a simulation involving two weakly exchanged-coupled spins with a g-factor difference of 1 MHz, of the same order as the Rabi frequency. We conclude that the narrow resonance is the result of driven transitions between the T- and T+ triplet states, using an ESR signal of frequency located halfway between the resonance frequencies of the two individual spins. The findings presented here offer an alternative method of implementing two-qubit gates, of relevance to the operation of larger scale spin qubit systems. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1608.07748v2-abstract-full').style.display = 'none'; document.getElementById('1608.07748v2-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 February, 2017; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 27 August, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. B 96, 045302 (2017) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1505.01213">arXiv:1505.01213</a> <span> [<a href="https://arxiv.org/pdf/1505.01213">pdf</a>, <a href="https://arxiv.org/format/1505.01213">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> </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.92.201401">10.1103/PhysRevB.92.201401 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Spin-orbit coupling and operation of multi-valley spin qubits </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Veldhorst%2C+M">M. Veldhorst</a>, <a href="/search/cond-mat?searchtype=author&query=Ruskov%2C+R">R. Ruskov</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Flatt%C3%A9%2C+M+E">M. E. Flatt茅</a>, <a href="/search/cond-mat?searchtype=author&query=Tahan%2C+C">C. Tahan</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1505.01213v1-abstract-short" style="display: inline;"> Spin qubits composed of either one or three electrons are realized in a quantum dot formed at a Si/SiO_2-interface in isotopically enriched silicon. Using pulsed electron spin resonance, we perform coherent control of both types of qubits, addressing them via an electric field dependent g-factor. We perform randomized benchmarking and find that both qubits can be operated with high fidelity. Surpr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1505.01213v1-abstract-full').style.display = 'inline'; document.getElementById('1505.01213v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1505.01213v1-abstract-full" style="display: none;"> Spin qubits composed of either one or three electrons are realized in a quantum dot formed at a Si/SiO_2-interface in isotopically enriched silicon. Using pulsed electron spin resonance, we perform coherent control of both types of qubits, addressing them via an electric field dependent g-factor. We perform randomized benchmarking and find that both qubits can be operated with high fidelity. Surprisingly, we find that the g-factors of the one-electron and three-electron qubits have an approximately linear but opposite dependence as a function of the applied dc electric field. We develop a theory to explain this g-factor behavior based on the spin-valley coupling that results from the sharp interface. The outer "shell" electron in the three-electron qubit exists in the higher of the two available conduction-band valley states, in contrast with the one-electron case, where the electron is in the lower valley. We formulate a modified effective mass theory and propose that inter-valley spin-flip tunneling dominates over intra-valley spin-flips in this system, leading to a direct correlation between the spin-orbit coupling parameters and the g-factors in the two valleys. In addition to offering all-electrical tuning for single-qubit gates, the g-factor physics revealed here for one-electron and three-electron qubits offers potential opportunities for new qubit control approaches. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1505.01213v1-abstract-full').style.display = 'none'; document.getElementById('1505.01213v1-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> 5 May, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. B 92, 201401 (2015) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1411.5760">arXiv:1411.5760</a> <span> [<a href="https://arxiv.org/pdf/1411.5760">pdf</a>, <a href="https://arxiv.org/format/1411.5760">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/10.1038/nature15263">10.1038/nature15263 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> A Two Qubit Logic Gate in Silicon </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Veldhorst%2C+M">M. Veldhorst</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Huang%2C+W">W. Huang</a>, <a href="/search/cond-mat?searchtype=author&query=Dehollain%2C+J+P">J. P. Dehollain</a>, <a href="/search/cond-mat?searchtype=author&query=Muhonen%2C+J+T">J. T. Muhonen</a>, <a href="/search/cond-mat?searchtype=author&query=Simmons%2C+S">S. Simmons</a>, <a href="/search/cond-mat?searchtype=author&query=Laucht%2C+A">A. Laucht</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1411.5760v1-abstract-short" style="display: inline;"> Quantum computation requires qubits that can be coupled and realized in a scalable manner, together with universal and high-fidelity one- and two-qubit logic gates \cite{DiVincenzo2000, Loss1998}. Strong effort across several fields have led to an impressive array of qubit realizations, including trapped ions \cite{Brown2011}, superconducting circuits \cite{Barends2014}, single photons\cite{Kok200… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1411.5760v1-abstract-full').style.display = 'inline'; document.getElementById('1411.5760v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1411.5760v1-abstract-full" style="display: none;"> Quantum computation requires qubits that can be coupled and realized in a scalable manner, together with universal and high-fidelity one- and two-qubit logic gates \cite{DiVincenzo2000, Loss1998}. Strong effort across several fields have led to an impressive array of qubit realizations, including trapped ions \cite{Brown2011}, superconducting circuits \cite{Barends2014}, single photons\cite{Kok2007}, single defects or atoms in diamond \cite{Waldherr2014, Dolde2014} and silicon \cite{Muhonen2014}, and semiconductor quantum dots \cite{Veldhorst2014}, all with single qubit fidelities exceeding the stringent thresholds required for fault-tolerant quantum computing \cite{Fowler2012}. Despite this, high-fidelity two-qubit gates in the solid-state that can be manufactured using standard lithographic techniques have so far been limited to superconducting qubits \cite{Barends2014}, as semiconductor systems have suffered from difficulties in coupling qubits and dephasing \cite{Nowack2011, Brunner2011, Shulman2012}. Here, we show that these issues can be eliminated altogether using single spins in isotopically enriched silicon\cite{Itoh2014} by demonstrating single- and two-qubit operations in a quantum dot system using the exchange interaction, as envisaged in the original Loss-DiVincenzo proposal \cite{Loss1998}. We realize CNOT gates via either controlled rotation (CROT) or controlled phase (CZ) operations combined with single-qubit operations. Direct gate-voltage control provides single-qubit addressability, together with a switchable exchange interaction that is employed in the two-qubit CZ gate. The speed of the two-qubit CZ operations is controlled electrically via the detuning energy and we find that over 100 two-qubit gates can be performed within a two-qubit coherence time of 8 \textmu s, thereby satisfying the criteria required for scalable quantum computation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1411.5760v1-abstract-full').style.display = 'none'; document.getElementById('1411.5760v1-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 November, 2014; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2014. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Full details, including two-qubit readout after CNOT operation, are in the published version: Nature 526, 410-414 (2015) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1407.1950">arXiv:1407.1950</a> <span> [<a href="https://arxiv.org/pdf/1407.1950">pdf</a>, <a href="https://arxiv.org/format/1407.1950">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> </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/nnano.2014.216">10.1038/nnano.2014.216 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> An addressable quantum dot qubit with fault-tolerant control fidelity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/cond-mat?searchtype=author&query=Veldhorst%2C+M">M. Veldhorst</a>, <a href="/search/cond-mat?searchtype=author&query=Hwang%2C+J+C+C">J. C. C. Hwang</a>, <a href="/search/cond-mat?searchtype=author&query=Yang%2C+C+H">C. H. Yang</a>, <a href="/search/cond-mat?searchtype=author&query=Leenstra%2C+A+W">A. W. Leenstra</a>, <a href="/search/cond-mat?searchtype=author&query=de+Ronde%2C+B">B. de Ronde</a>, <a href="/search/cond-mat?searchtype=author&query=Dehollain%2C+J+P">J. P. Dehollain</a>, <a href="/search/cond-mat?searchtype=author&query=Muhonen%2C+J+T">J. T. Muhonen</a>, <a href="/search/cond-mat?searchtype=author&query=Hudson%2C+F+E">F. E. Hudson</a>, <a href="/search/cond-mat?searchtype=author&query=Itoh%2C+K+M">K. M. Itoh</a>, <a href="/search/cond-mat?searchtype=author&query=Morello%2C+A">A. Morello</a>, <a href="/search/cond-mat?searchtype=author&query=Dzurak%2C+A+S">A. S. Dzurak</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="1407.1950v1-abstract-short" style="display: inline;"> Exciting progress towards spin-based quantum computing has recently been made with qubits realized using nitrogen-vacancy (N-V) centers in diamond and phosphorus atoms in silicon, including the demonstration of long coherence times made possible by the presence of spin-free isotopes of carbon and silicon. However, despite promising single-atom nanotechnologies, there remain substantial challenges… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1407.1950v1-abstract-full').style.display = 'inline'; document.getElementById('1407.1950v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1407.1950v1-abstract-full" style="display: none;"> Exciting progress towards spin-based quantum computing has recently been made with qubits realized using nitrogen-vacancy (N-V) centers in diamond and phosphorus atoms in silicon, including the demonstration of long coherence times made possible by the presence of spin-free isotopes of carbon and silicon. However, despite promising single-atom nanotechnologies, there remain substantial challenges in coupling such qubits and addressing them individually. Conversely, lithographically defined quantum dots have an exchange coupling that can be precisely engineered, but strong coupling to noise has severely limited their dephasing times and control fidelities. Here we combine the best aspects of both spin qubit schemes and demonstrate a gate-addressable quantum dot qubit in isotopically engineered silicon with a control fidelity of 99.6%, obtained via Clifford based randomized benchmarking and consistent with that required for fault-tolerant quantum computing. This qubit has orders of magnitude improved coherence times compared with other quantum dot qubits, with T_2* = 120 mus and T_2 = 28 ms. By gate-voltage tuning of the electron g*-factor, we can Stark shift the electron spin resonance (ESR) frequency by more than 3000 times the 2.4 kHz ESR linewidth, providing a direct path to large-scale arrays of addressable high-fidelity qubits that are compatible with existing manufacturing technologies. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1407.1950v1-abstract-full').style.display = 'none'; document.getElementById('1407.1950v1-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 July, 2014; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2014. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Nature Nanotechnology 9, 981 (2014) </p> </li> </ol> <div class="is-hidden-tablet">  <span class="help" style="display: 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