Electron readout contrast enhancement in the parallel nuclear regime of an exchange-coupled donor spin qubit system

TL;DR

This paper analyzes why electron readout contrast increases in exchange-coupled donor spin qubits in silicon when donor nuclei are in a parallel spin state, attributing it to an additional tunneling event during readout.

Contribution

It provides a detailed physical explanation for the contrast enhancement phenomenon in parallel nuclear regimes of donor spin qubits, improving understanding of spin-dependent tunneling.

Findings

Enhanced readout contrast linked to an extra tunneling event during measurement

Parallel nuclear spin alignment increases electron tunneling probability

Insights can improve readout fidelity in donor-based qubits

Abstract

Recent experiments on donor-based spin qubits in silicon have leveraged the exchange interaction between electrons bound to separate donor nuclei to perform two-qubit operations. A consistently observed yet unexplained phenomenon in such systems is the significant increase in electron readout contrast, measured via Elzerman-style readout to a single-electron transistor (SET) island, when the donor nuclei are initialized in a parallel spin orientation compared to an anti-parallel orientation. In this work, we present a detailed analysis of the exchange-coupled donor system in the parallel nuclear regime and propose a physical mechanism for this effect. We attribute the enhanced readout contrast to an additional electron tunneling event to the SET during a single read period, when the donor nuclei are aligned in a parallel spin configuration. These insights inform strategies for improving electron readout fidelity in these systems and contribute to a more complete understanding of spin-dependent tunnelling processes in donor-based qubit architectures.