Observation of extremely slow hole spin relaxation in self-assembled quantum dots

TL;DR

This study demonstrates that hole spins in self-assembled quantum dots relax extremely slowly, over hundreds of microseconds, with relaxation dynamics influenced by magnetic field and temperature, highlighting potential for quantum information storage.

Contribution

It provides the first experimental measurement of long hole spin relaxation times in strongly confined quantum dots, supported by theoretical calculations.

Findings

Hole spin relaxation times up to ~270 microseconds.

Relaxation dynamics depend on magnetic field and temperature.

Spin relaxation is mediated by spin-orbit phonon scattering.

Abstract

We report the measurement of extremely slow hole spin relaxation dynamics in small ensembles of self-assembled InGaAs quantum dots. Individual spin orientated holes are optically created in the lowest orbital state of each dot and read out after a defined storage time using spin memory devices. The resulting luminescence signal exhibits a pronounced polarization memory effect that vanishes for long storage times. The hole spin relaxation dynamics are measured as a function of external magnetic field and lattice temperature. We show that hole spin relaxation can occur over remarkably long timescales in strongly confined quantum dots (up to ~270 us), as predicted by recent theory. Our findings are supported by calculations that reproduce both the observed magnetic field and temperature dependencies. The results suggest that hole spin relaxation in strongly confined quantum dots is due to spin orbit mediated phonon scattering between Zeeman levels, in marked contrast to higher dimensional nanostructures where it is limited by valence band mixing.