Gate fidelity and coherence of an electron spin in a Si/SiGe quantum dot with micromagnet

TL;DR

This study demonstrates high-fidelity control and long coherence times of an electron spin qubit in Si/SiGe quantum dots with micromagnet control, highlighting its potential for quantum computing and memory applications.

Contribution

It presents the first detailed measurement of gate fidelity and coherence times of an electron spin qubit in Si/SiGe quantum dots with micromagnet control, showing promising performance without isotopic purification.

Findings

Achieved ~99% single-qubit gate fidelity.

Extended coherence time up to 400 μs with dynamical decoupling.

Identified charge noise as a potential limit to coherence.

Abstract

The gate fidelity and the coherence time of a qubit are important benchmarks for quantum computation. We construct a qubit using a single electron spin in a Si/SiGe quantum dot and control it electrically via an artificial spin-orbit field from a micromagnet. We measure an average single-qubit gate fidelity of $\approx$ 99$\%$ using randomized benchmarking, which is consistent with dephasing from the slowly evolving nuclear spins in substrate. The coherence time measured using dynamical decoupling extends up to $\approx$ 400 $\mu$s for 128 decoupling pulses, with no sign of saturation. We find evidence that the coherence time is limited by noise in the 10 kHz $-$ 1 MHz range, possibly because charge noise affecting the spin via the micromagnet gradient. This work shows that an electron spin in a Si/SiGe quantum dot is a good candidate for quantum information processing as well as for a quantum memory, even without isotopic purification.