Spin qubits made of quantum dots and donors in silicon

In this talk, I will present our recent work on control and readout of electron spin qubits in silicon MOS. Valley splitting is an issue that can induce control variability or limit readout fidelity. We show how this splitting is tunable in MOS devices [1], and introduce a shell-filling trick to overcome potential readout challenges. Readout fidelity has lagged behind that of control. We demonstrate that an enhanced latching mechanism can be used to improve the signal and lifetime of the spin-blockade readout while preserving its speed, achieving single-shot readout fidelities of > 99.86% [2]. The best spin qubit in the solid state is the nuclear spin of donors, but it is difficult to couple it to other qubits. We show coherent coupling of a donor to a quantum dot, a milestone for nuclear spin quantum computing [3]. We also study spin-orbit interaction for electrons in silicon quantum dots. We show that it is sufficiently large to drive a singlet-triplet qubit, allowing universal control without external elements [4]. We study the mechanisms behind this interaction and find three different effects [5]. Our work identifies crystallographic and magnetic field anisotropies that can be used to enhance or suppress these effects.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the DOE’s National Nuclear Security Administration under contract DE-NA0003525. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government.

[1] Gamble et al., App. Phys. Lett. 109, 253101 (2016)
[2] Harvey-Collard et al., Phys. Rev. X (2018)
[3] Harvey-Collard et al., Nat. Comm. 8, 1029 (2017)
[4] Jock et al., Nat. Comm. 9, 1768 (2018)
[5] Harvey-Collard et al., arXiv:1808.07378 (2018)