A >99.9%-fidelity quantum-dot spin qubit with coherence limited by charge noise

TL;DR

This paper demonstrates a high-fidelity single-electron spin qubit with coherence limited by charge noise, highlighting the importance of charge noise considerations in designing scalable spin-qubit systems.

Contribution

It reports a spin qubit with >99.9% fidelity and coherence limited by charge noise, emphasizing the role of charge noise in qubit design and control.

Findings

Coherence time of 20 microseconds achieved

Single-qubit gate fidelities exceed 99.9%

Charge noise with 1/f spectrum limits dephasing

Abstract

Recent advances towards spin-based quantum computation have been primarily fuelled by elaborate isolation from noise sources, such as surrounding nuclear spins and spin-electric susceptibility, to extend spin coherence. In the meanwhile, addressable single-spin and spin-spin manipulations in multiple-qubit systems will necessitate sizable spin-electric coupling. Given background charge fluctuation in nanostructures, however, its compatibility with enhanced coherence should be crucially questioned. Here we realise a single-electron spin qubit with isotopically-enriched phase coherence time (20 microseconds) and fast electrical control speed (up to 30 MHz) mediated by extrinsic spin-electric coupling. Using rapid spin rotations, we reveal that the free-evolution dephasing is caused by charge (instead of conventional magnetic) noise featured by a 1/f spectrum over seven decades of frequency. The qubit nevertheless exhibits superior performance with single-qubit gate fidelities exceeding 99.9% on average. Our work strongly suggests that designing artificial spin-electric coupling with account taken of charge noise is a promising route to large-scale spin-qubit systems having fault-tolerant controllability.