Dynamics of a mesoscopic nuclear spin ensemble interacting with an optically driven electron spin

TL;DR

This paper investigates the dynamics of nuclear spin environments in quantum dots using all-optical resonance fluorescence, revealing how local magnetic fluctuations and nuclear spin interactions depend on optical probing conditions.

Contribution

It introduces a novel all-optical sensing method to distinguish magnetic noise sources and characterizes nuclear spin bath dynamics under different optical saturation levels.

Findings

Nuclear spin fluctuations have two correlation times in the microsecond range.

Correlation times increase with optical saturation, indicating motional averaging effects.

Local magnetic field fluctuations are influenced by optically driven electron spin flips.

Abstract

The ability to discriminate between simultaneously occurring noise sources in the local environment of semiconductor InGaAs quantum dots, such as electric and magnetic field fluctuations, is key to understanding their respective dynamics and their effect on quantum dot coherence properties. We present a discriminatory approach to all-optical sensing based on two-color resonance fluorescence of a quantum dot charged with a single electron. Our measurements show that local magnetic field fluctuations due to nuclear spins in the absence of an external magnetic field are described by two correlation times, both in the microsecond regime. The nuclear spin bath dynamics show a strong dependence on the strength of resonant probing, with correlation times increasing by a factor of four as the optical transition is saturated. We interpret the behavior as motional averaging of both the Knight field of the resident electron spin and the hyperfine-mediated nuclear spin-spin interaction due to optically-induced electron spin flips.