Polarization freezing of 10000 optically-cooled nuclear spins by coupling to a single electron

TL;DR

This paper demonstrates that a single optically controlled electron spin in a quantum dot can significantly extend the coherence time of surrounding nuclear spins, achieving decay times over 100 seconds by suppressing depolarization.

Contribution

It introduces a method to freeze nuclear spin polarization using a single electron spin, revealing a new way to enhance quantum memory stability in solid-state systems.

Findings

Nuclear spin decay time exceeds 100 seconds at low temperatures.

Optical initialization of nuclear spins occurs within milliseconds.

Long nuclear spin lifetimes are due to Knight field effects.

Abstract

The nature of the nano-scale environment presents a major challenge for solid-state implementation of spin-based qubits. In this work, a single electron spin in an optically pumped nanometer-sized III-V semiconductor quantum dot is used to control a macroscopic nuclear spin of several thousand nuclei, freezing its decay and leading to spin life-times exceeding 100 seconds at low temperatures. Few-millisecond-fast optical initialization of the nuclear spin is followed by a slow decay exhibiting random telegraph signals at long delay times, arising from low probability electron jumps out of the dot. The remarkably long spin life-time in a dot surrounded by a densely-packed nuclear spin environment arises from the Knight field created by the resident electron, which leads to suppression of nuclear spin depolarization.