Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot

TL;DR

This paper demonstrates a long-lived, electrically controlled spin qubit in a Si/SiGe quantum dot with coherence times significantly longer than in III-V quantum dots, advancing scalable quantum computing prospects.

Contribution

The authors achieve all-electrical two-axis control of a silicon spin qubit with coherence times nearly two orders of magnitude longer than previous III-V quantum dots.

Findings

Ramsey decay time of 1 microsecond

Hahn echo decay time of 40 microseconds

Qubit operation times comparable to GaAs

Abstract

Nanofabricated quantum bits permit large-scale integration but usually suffer from short coherence times due to interactions with their solid-state environment. The outstanding challenge is to engineer the environment so that it minimally affects the qubit, but still allows qubit control and scalability. Here we demonstrate a long-lived single-electron spin qubit in a Si/SiGe quantum dot with all-electrical two-axis control. The spin is driven by resonant microwave electric fields in a transverse magnetic field gradient from a local micromagnet, and the spin state is read out in single-shot mode. Electron spin resonance occurs at two closely spaced frequencies, which we attribute to two valley states. Thanks to the weak hyperfine coupling in silicon, Ramsey and Hahn echo decay timescales of 1us and 40us, respectively, are observed. This is almost two orders of magnitude longer than the intrinsic timescales in III-V quantum dots, while gate operation times are comparable to those achieved in GaAs. This places the single-qubit rotations in the fault-tolerant regime and strongly raises the prospects of quantum information processing based on quantum dots.