Depolarization of Electronic Spin Qubits Confined in Semiconductor Quantum Dots

TL;DR

This study investigates spin relaxation in various electronic spin qubits within a single quantum dot, revealing that heavy holes and dark excitons have longer coherence times due to hyperfine interactions and exchange effects.

Contribution

It provides the first comprehensive comparison of spin relaxation across multiple charge carriers in the same quantum dot using all optical techniques.

Findings

Heavy holes dephase slower than electrons.

Dark excitons have longer coherence times than heavy holes.

Spin relaxation aligns with central spin theory involving hyperfine interactions.

Abstract

Quantum dots are arguably the best interface between matter spin qubits and flying photonic qubits. Using quantum dot devices to produce joint spin-photonic states requires the electronic spin qubits to be stored for extended times. Therefore, the study of the coherence of spins of various quantum dot confined charge carriers is important both scientifically and technologically. In this study we report on spin relaxation measurements performed on five different forms of electronic spin qubits confined in the very same quantum dot. In particular, we use all optical techniques to measure the spin relaxation of the confined heavy hole and that of the dark exciton - a long lived electron-heavy hole pair with parallel spins. Our measured results for the spin relaxation of the electron, the heavy-hole, the dark exciton, the negative and the positive trions, in the absence of externally applied magnetic field, are in agreement with a central spin theory which attributes the dephasing of the carriers' spin to their hyperfine interactions with the nuclear spins of the atoms forming the quantum dots. We demonstrate that the heavy hole dephases much slower than the electron. We also show, both experimentally and theoretically, that the dark exciton dephases slower than the heavy hole, due to the electron-hole exchange interaction, which partially protects its spin state from dephasing.