Long nuclear spin decay times controlled by optical pumping in individual quantum dots

TL;DR

This study demonstrates control over nuclear spin decay times in quantum dots through optical pumping, revealing long decay times due to spin diffusion and enabling detection of unstable polarization states.

Contribution

It introduces a method to control and measure nuclear spin decay times in quantum dots, highlighting the role of spin diffusion and bi-stability in nuclear polarization dynamics.

Findings

Nuclear spin decay times range from 0.2 to 5 seconds.

Long decay times are due to spin diffusion into surrounding material.

Time-resolved methods detect unstable polarization states.

Abstract

Nuclear polarization dynamics are measured in the nuclear spin bi-stability regime in a single optically pumped InGaAs/GaAs quantum dot. The controlling role of nuclear spin diffusion from the dot into the surrounding material is revealed in pump-probe measurements of the non-linear nuclear spin dynamics. We measure nuclear spin decay times in the range 0.2-5 sec, strongly dependent on the optical pumping time. The long nuclear spin decay arises from polarization of the material surrounding the dot by spin diffusion for long (>5sec) pumping times. The time-resolved methods allow the detection of the unstable nuclear polarization state in the bi-stability regime otherwise undetectable in cw experiments.