Intrinsic limit to electron spin coherence in InGaAs quantum dots featuring strain-induced nuclear dispersion

TL;DR

This study reveals that the intrinsic limit to electron spin coherence in InGaAs quantum dots is set by strain-induced nuclear quadrupolar effects, and introduces an all-optical method to measure spin coherence without disturbing the nuclear environment.

Contribution

The paper develops a non-perturbative optical technique to measure electron spin coherence and identifies strain-induced quadrupolar interactions as the fundamental decoherence source.

Findings

Achieved Hahn-echo decoupling to reach the intrinsic coherence limit.

Identified strain-induced quadrupolar broadening as the main decoherence mechanism.

Demonstrated that reducing strain could extend electron spin coherence times.

Abstract

The Zeeman-split spin-states of a single electron confined in a self-assembled quantum dot provide an optically-accessible spin qubit. For III-V materials the nuclear spins of the solid-state host provide an intrinsic noise source, resulting in electron-spin dephasing times of few nanoseconds. While a comprehensive study of electron-spin dynamics at low magnetic field has recently been carried out, what limits the electron coherence in these systems remains unclear, in part due to the dominant effect of measurement-induced dynamic polarisation of the nuclear bath. We develop an all-optical method to access the quantum dot spin-state without perturbing the nuclear environment. We use this method to implement Hahn-echo decoupling and reach the intrinsic limit to coherence set by inhomogeneous strain fields coupling to quadrupolar moments of the nuclear bath. These results indicate that the extension of electron spin coherence beyond this few-microsecond limit necessitates the reduction of strain-induced quadrupolar broadening in these materials.