Quantum bath-driven decoherence of mixed spin systems

TL;DR

This paper develops a comprehensive theoretical framework for understanding quantum bath-driven decoherence in mixed spin systems, validated by experiments on bismuth donors in silicon and comparisons with previous data.

Contribution

It introduces a general analytical expression for decoherence times that distinguishes quantum bath effects from classical noise, supported by experimental and simulation validation.

Findings

Excellent agreement between theory and ESR/NMR measurements

Validation of the theory at optimal working points with suppressed decoherence

Quantitative match with cluster expansion simulations

Abstract

The decoherence of mixed electron-nuclear spin qubits is a topic of great current importance, but understanding is still lacking: while important decoherence mechanisms for spin qubits arise from quantum spin bath environments with slow decay of correlations, the only analytical framework for explaining observed sharp variations of decoherence times with magnetic field is based on the suppression of classical noise. Here we obtain a general expression for decoherence times of the central spin system which exposes significant differences between quantum-bath decoherence and decoherence by classical field noise. We perform measurements of decoherence times of bismuth donors in natural silicon using both electron spin resonance (ESR) and nuclear magnetic resonance (NMR) transitions, and in both cases find excellent agreement with our theory across a wide parameter range. The universality of our expression is also tested by quantitative comparisons with previous measurements of decoherence around `optimal working points' or `clock transitions' where decoherence is strongly suppressed. We further validate our results by comparison to cluster expansion simulations.