Theory of coherent spin transfer between two semiconductor quantum dots*

Long-distance transfer of quantum information in quantum dots (QDs) spin qubits will be necessary for their scalability [1]. One way of achieving this goal is to move the electron between tunnel-coupled QDs using a sweep of their energy detuning [2, 3]. We present here an analysis showing how coherent transfer of spin superposition is affected by electron-phonon scattering and charge noise in detuning and tunnel coupling at finite temperature. We have predicted that probability of charge transfer can be non-monotonic function of transfer time, and predicted that the error below 0.001 requires tunnel couplings above 20µeV, as it has been confirmed experimentally in Si/SiGe [3] and SiMOS [4]. Next we analyzed to what extent electron transfer modifies the spin coherence and uncovered that in absence of nuclear spins, main dephasing mechanisms are activated by a difference of Zeeman splittings in the QDs, which leads to: short-term creation of charge qubit and random phase rotation during temporal occupation of higher energy state.

[1] L.M.K. Vandersypen et al., npj Quantum Information 3, 34 (2017)

[2] T. A. Baart et al., Nature Nanotechnology 11, 330-334 (2016)

[3] A. R. Mills et al., Nature Communications 10, 1063 (2019)

[4] J. Yoneda et al., Nature Communications 12, 4114 (2021)