Coherence and Screening in Multi-Electron Spin Qubits

TL;DR

This paper compares the coherence properties of multi-electron and single-electron spin qubits, revealing enhanced performance in multi-electron systems with faster exchange oscillations and providing a dephasing model that accounts for noise sources.

Contribution

It introduces a comparative analysis of exchange oscillations in multi-electron versus single-electron quantum dots and develops a dephasing model incorporating voltage and hyperfine noise.

Findings

Multi-electron qubits exhibit >1 GHz exchange oscillations with Q > 15.

Single-electron qubits show Q ~ 2, consistent with previous results.

A dephasing model including voltage and hyperfine noise matches experimental data.

Abstract

The performance of multi-electron spin qubits is examined by comparing exchange oscillations in coupled single-electron and multi-electron quantum dots in the same device. Fast (> 1 GHz) exchange oscillations with a quality factor Q > 15 are found for the multi-electron case, compared to Q ~ 2 for the single-electron case, the latter consistent with previous experiments. A model of dephasing that includes voltage and hyperfine noise is developed that is in good agreement with both single- and multi-electron data, though in both cases additional exchange-independent dephasing is needed to obtain quantitative agreement across a broad parameter range.