Direct Measurement of Quantum Dot Spin Dynamics using Time-Resolved Resonance Fluorescence

TL;DR

This study directly measures the spin dynamics of a quantum dot electron using time-resolved resonance fluorescence, revealing key timescales and mechanisms of spin initialization and relaxation under varying magnetic fields.

Contribution

It provides the first direct optical measurement of quantum dot spin initialization and relaxation timescales, and identifies the magnetic field-dependent mechanisms affecting spin-flip processes.

Findings

Spin initialization occurs in microseconds under resonant laser excitation.

Spin relaxation times are on the order of milliseconds.

The spin-flip mechanism shifts from electron-nuclei to hole-mixing at 0.6 Tesla.

Abstract

We temporally resolve the resonance fluorescence from an electron spin confined to a single self-assembled quantum dot to measure directly the spin's optical initialization and natural relaxation timescales. Our measurements demonstrate that spin initialization occurs on the order of microseconds in the Faraday configuration when a laser resonantly drives the quantum dot transition. We show that the mechanism mediating the optically induced spin-flip changes from electron-nuclei interaction to hole-mixing interaction at 0.6 Tesla external magnetic field. Spin relaxation measurements result in times on the order of milliseconds and suggest that a $B^{-5}$ magnetic field dependence, due to spin-orbit coupling, is sustained all the way down to 2.2 Tesla.