Probing the Variation of the Intervalley Tunnel Coupling in a Silicon Triple Quantum Dot

Borjans, Felix; Zhang, X.; Mi, Xiao; Cheng, Guangming; Yao, Nan; Jackson, Clayton A.; Edge, L. F.; Petta, J. R.

doi:10.1103/prxquantum.2.020309

Cited by 23 publications

(21 citation statements)

References 59 publications

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“…Of course, γ must be positive in order to properly simulate leakage, else the probability would increase exponentially with time. Based on recent experimental results [13], we estimate γ to be no greater than one tenth the value of the nearest-neighbor coupling strength J 1 , perhaps even much smaller.…”

Section: Modelmentioning

confidence: 60%

Dissipation and gate timing errors in SWAP operations of qubits

Foulk,

Throckmorton,

Sarma

2021

Preprint

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We investigate the fidelity of a sequence of SWAP gates on a Si-based quantum dot (QD) spin qubit chain. We particularly examine how valley leakage and gate timing error affect the gate fidelity compared to charge noise, which is always present. In our Hamiltonian, each qubit is coupled via Heisenberg exchange to every other qubit in the chain, with the strength of the exchange interaction decreasing exponentially with qubit distance. Valley leakage is modeled through a dissipation term γ as appropriate for the experimentally observed intervalley tunneling effect. We show that randomness in the valley leakage parameter has little to no effect on the SWAP gate fidelity in the currently fabricated Si circuits. We introduce disorder in the forms of charge noise and gate timing error and average the fidelities of 10,000 calculations for each set of parameters. The fidelities are then plotted against JSWAP, the strength of the exchange coupling corresponding to the SWAP gate. We find that valley leakage decreases the fidelity of the SWAP operation-though the effect is small compared to that of the known charge noise-and that gate timing error creates an effective optimal value of JSWAP, beyond which infidelity begins to increase.

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Section: Modelmentioning

confidence: 60%

Dissipation and gate timing errors in SWAP operations of qubits

Foulk,

Throckmorton,

Sarma

2021

Preprint

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“…The problem with having multiple valley states is that their presence can lead to leakage out of the computational space if the valley degeneracy is not adequately broken. Of the six valley states present in bulk Silicon, four of these decouple when strain is applied to the sample, but the degeneracy of the final two valley states is broken only by a small valley splitting term that is dependent on the microscopics of the system [24]. We emphasize that there is no known way to control this valley splitting in specific qubits, and in fact, one can figure out the size of the valley splitting only aposteriori.…”

Section: Introductionmentioning

confidence: 94%

Spin-Valley Qubit Dynamics in Exchange-Coupled Silicon Quantum Dots

Buterakos

Sarma

2021

PRX Quantum

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The presence of valley states is a significant obstacle to realizing quantum information technologies in Silicon quantum dots, as leakage into alternate valley states can introduce errors into the computation. We use a perturbative analytical approach to study the dynamics of exchange-coupled quantum dots with valley degrees of freedom. We show that if the valley splitting is large and electrons are not properly initialized to valley eigenstates, then time evolution of the system will lead to spin-valley entanglement. Spin-valley entanglement will also occur if the valley splitting is small and electrons are not initialized to the same valley state. Additionally, we show that for small valley splitting, spin-valley entanglement does not affect measurement probabilities of two-qubit systems; however, systems with more qubits will be affected. This means that two-qubit gate fidelities measured in two-qubit systems may miss the effects of valley degrees of freedom. Our work shows how the existence of valleys may adversely affect multiqubit fidelities even when the system temperature is very low.

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“…The electrostatic and magnetic environment of the shuttling chain can be accurately engineered, or at least known, to good accuracy. However, the variation in the valley parameters ∆ d is believed to be large on account of their sensitivity to microscopic interface details [72], and experiment is just beginning to probe the variation in inter-and intra-valley tunnel couplings in silicon quantum dot arrays [73].…”

Section: Shuttlingmentioning

confidence: 99%

Multicore Quantum Computing

Jnane,

Undseth,

Cai

et al. 2022

Preprint

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Any architecture for practical quantum computing must be scalable. An attractive approach is to create multiple cores, computing regions of fixed size that are well-spaced but interlinked with communication channels. This exploded architecture can relax the demands associated with a single monolithic device: the complexity of control, cooling and power infrastructure as well as the difficulties of cross-talk suppression and near-perfect component yield. Here we explore interlinked multicore architectures through analytic and numerical modelling. While elements of our analysis are relevant to diverse platforms, our focus is on semiconductor electron spin systems in which numerous cores may exist on a single chip. We model shuttling and microwave-based interlinks and estimate the achievable fidelities, finding values that are encouraging but markedly inferior to intra-core operations. We therefore introduce optimsed entanglement purification to enable highfidelity communication, finding that 99.5% is a very realistic goal. We then assess the prospects for quantum advantage using such devices in the NISQ-era and beyond: we simulate recently proposed exponentially-powerful error mitigation schemes in the multicore environment and conclude that these techniques impressively suppress imperfections in both the inter-and intra-core operations.

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Probing the Variation of the Intervalley Tunnel Coupling in a Silicon Triple Quantum Dot

Cited by 23 publications

References 59 publications

Dissipation and gate timing errors in SWAP operations of qubits

Dissipation and gate timing errors in SWAP operations of qubits

Spin-Valley Qubit Dynamics in Exchange-Coupled Silicon Quantum Dots

Multicore Quantum Computing

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