Intrinsic spin fluctuations reveal the dynamical response function of holes coupled to nuclear spin baths in (In,Ga)As quantum dots

TL;DR

This study uses intrinsic spin fluctuations in (In,Ga)As quantum dots to uncover the dynamical response of holes interacting with nuclear spin baths, revealing long correlation times and a crossover in relaxation dynamics.

Contribution

It introduces a novel method of using spin noise to directly measure the dynamical response function of hole-nuclear spin interactions in quantum dots.

Findings

Spin correlation times extend to 400 ns at zero field and up to 5 μs with small magnetic fields.

The noise lineshape transitions from Lorentzian to power-law, indicating a change from exponential to inverse-log relaxation.

Longer spin correlation times suggest potential for quantum information applications.

Abstract

The problem of how single "central" spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying timescales and dynamical responses (exponential, power-law, Gaussian, etc). Here we detect the small random fluctuations of central spins in thermal equilibrium (holes in singly-charged (In,Ga)As quantum dots) to reveal the timescales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at zero magnetic field, that increase to $\sim$5 $\mu$s as hole-nuclear coupling is suppressed with small (100 G) applied fields. Concomitantly, the noise lineshape evolves from Lorentzian to power-law, indicating a crossover from exponential to inverse-log dynamics.