Theory of coherent electron shuttling using pre-defined and moving quantum dots in Si

Coherent electron shuttling can improve design of scalable quantum computers [1]. We have identified challenges in two shuttling modes: Bucket Brigade (BB) and Conveyor Belt (CB). In BB, the electron is moved using sequential dot-to-dot adiabatic transition. By considering realistic environment of Si QDs, we have found single transition error to be non-monotonic function of sweep rate. We have found an optimal sweep rate, at which transfer fidelity can exceed 99.9%, provided tunnel-coupling induced gap at zero detuning t_c>30μeV [2,3]. However having uniform t_c in long QDs array might be hard to achieve.

In contrast in CB mode, 4-terminal gates are proven to generate stable and deep moving potential, even in presence of typical electrostatic disorder [4,5]. With high-fidelity charge transfer, we have analyzed the spin dynamics and predicted 99.9% fidelity of coherent transfer over 10μm at ≈10 m/s electron velocity. The remaining error is attributed to spin dephasing, which is activated by: valley excitations on atomistic disorder and spatially dependent fluctuations of spin splitting from nuclear spins or charge noise.

[1] J.M. Boter et al., Phys. Rev. App. 18, 024053 (2022)

[2] J.A.K, L. Cywinski, Phys. Rev. B 101, 035303 (2020)

[3] J.A.K, L. Cywinski, Phys. Rev. B 104, 075439 (2021)

[4] I. Seidler et al., npj Quantum Information 8, 100 (2021)

[5] V. Langrock, J.A.K et al., arXiv:2202.11793