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

Buterakos, Donovan; Sarma, Sankar Das

doi:10.1103/prxquantum.2.040358

Cited by 11 publications

(8 citation statements)

References 39 publications

(33 reference statements)

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“…Such a variation means that as we shuttle the spin qubit from one dot to another, the spin qubit may interact with the excited orbitals in the two dots, resulting in a state that has qubit information leaked into the excited orbital. Such a leaked component is analogous to a spin qubit with a miscalibrated detuning, thus its interaction with the other qubits will also be erroneous [58]. A typical value assumed for the inter-valley relaxation time is ∼ 100 ns [55], and it can go as low as 10 ns [59,60].…”

Section: B Threshold Calculationsmentioning

confidence: 99%

Looped Pipelines Enabling Effective 3D Qubit Lattices in a Strictly 2D Device

Cai¹,

Siegel²,

Benjamin³

2022

Preprint

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Many quantum computing platforms are based on a fundamentally two-dimensional physical layout. However, there are advantages (for example in fault-tolerant systems) to having a 3D architecture. Here we explore a concept called looped pipelines which permits one to obtain many of the advantages of a 3D lattice while operating a strictly 2D device. The concept leverages qubit shuttling, a well-established feature in platforms like semiconductor spin qubits and trappedion qubits. The looped pipeline architecture has similar hardware requirements to other shuttling approaches, but can process a stack of qubit arrays instead of just one. Simple patterns of intra-and inter-loop interactions allow one to embody diverse schemes from NISQ-era error mitigation through to fault-tolerant codes. For the former, protocols involving multiple states can be implemented with a similar space-time resource as preparing one noisy copy. For the latter, one can realise a far broader variety of code structures; in particular, we consider a stack of 2D codes within which transversal CNOTs are available. We find that this can achieve a cost saving of up to a factor of ∼ 80 in the space-time overhead for magic state distillation (and a factor of ∼ 200 with modest additional hardware). Using numerical modelling and experimentally-motivated noise models we verify that the looped pipeline approach provides these benefits without significant reduction in the code's threshold.

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Section: B Threshold Calculationsmentioning

confidence: 99%

Looped Pipelines Enabling Effective 3D Qubit Lattices in a Strictly 2D Device

Cai¹,

Siegel²,

Benjamin³

2022

Preprint

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“…While long coherence times 9 and high fidelity gates [10][11][12][13] have been achieved, there are concerns about how the valley degree of freedom may impact performance as the number of silicon spin qubits scales up. 14,15 The strain of the Si quantum well (QW) induced by the Si and SiGe lattice mismatch partially lifts the six-fold valley degeneracy present in bulk Si. 16 However, failure to lift the degeneracy of the low lying ±z-valleys can lead to an additional uncontrolled degree of freedom [17][18][19] and fast qubit relaxation.…”

Section: Introductionmentioning

confidence: 99%

Microwave-frequency scanning gate microscopy of a Si/SiGe double quantum dot

Denisov,

Oh,

Fuchs

et al. 2022

Preprint

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Conventional quantum transport methods can provide quantitative information on spin, orbital, and valley states in quantum dots, but often lack spatial resolution. Scanning tunneling microscopy, on the other hand, provides exquisite spatial resolution of the local electronic density of states, but often at the expense of speed. Working to combine the spatial resolution and energy sensitivity of scanning probe microscopy with the speed of microwave measurements, we couple a metallic probe tip to a Si/SiGe double quantum dot that is integrated with a local charge detector. We first demonstrate that a dc-biased tip can be used to change the charge occupancy of the double dot. We then apply microwave excitation through the scanning tip to drive photonassisted tunneling transitions in the double dot. We infer the double dot energy level diagram from the frequency and detuning dependence of the photon-assisted tunneling resonance condition. These measurements allow us to resolve ∼65 µeV excited states, an energy scale con-sistent with typical valley splittings in Si/SiGe. Future extensions of this approach may allow spatial mapping of the valley splitting in Si devices, which is of fundamental importance for spin-based quantum processors.

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“…While long coherence times 8 and high fidelity gates 9−12 have been achieved, there are concerns about how the valley degree of freedom, as well as charge and magnetic disorder, will impact performance as the number of silicon spin qubits scales up. 13,14 Other concerns are related to the tuning and readout 15 of 2D spin qubit arrays. 16 Each outlined challenge demands spatial resolution and may be suitably addressed with different variations of scanning probe microscopy.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Silicon spin qubits are among the leading contenders for building fault-tolerant quantum computers , due to their small ∼100 nm footprint and the ability to chemically and isotopically purify the silicon host material. While long coherence times and high fidelity gates − have been achieved, there are concerns about how the valley degree of freedom, as well as charge and magnetic disorder, will impact performance as the number of silicon spin qubits scales up. , Other concerns are related to the tuning and readout of 2D spin qubit arrays . Each outlined challenge demands spatial resolution and may be suitably addressed with different variations of scanning probe microscopy.…”

Section: Introductionmentioning

confidence: 99%

Microwave-Frequency Scanning Gate Microscopy of a Si/SiGe Double Quantum Dot

Gordian

et al. 2022

Nano Lett.

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Conventional transport methods provide quantitative information on spin, orbital, and valley states in quantum dots but lack spatial resolution. Scanning tunneling microscopy, on the other hand, provides exquisite spatial resolution at the expense of speed. Working to combine the spatial resolution and energy sensitivity of scanning probe microscopy with the speed of microwave measurements, we couple a metallic tip to a Si/SiGe double quantum dot (DQD) that is integrated with a charge detector. We first demonstrate that the dc-biased tip can be used to change the occupancy of the DQD. We then apply microwaves through the tip to drive photon-assisted tunneling (PAT). We infer the DQD level diagram from the frequency and detuning dependence of the tunneling resonances. These measurements allow the resolution of ∼65 μeV excited states, an energy consistent with valley splittings in Si/SiGe. This work demonstrates the feasibility of scanning gate experiments with Si/SiGe devices.

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

Cited by 11 publications

References 39 publications

Looped Pipelines Enabling Effective 3D Qubit Lattices in a Strictly 2D Device

Looped Pipelines Enabling Effective 3D Qubit Lattices in a Strictly 2D Device

Microwave-frequency scanning gate microscopy of a Si/SiGe double quantum dot

Microwave-Frequency Scanning Gate Microscopy of a Si/SiGe Double Quantum Dot

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