Controlling a mesoscopic spin environment by quantum bit manipulation

TL;DR

This paper introduces a method to control and utilize mesoscopic nuclear spin environments via a quantum bit, enabling long-lived quantum memory and coherent manipulation despite low polarization.

Contribution

It provides a unified theoretical framework for cooling and controlling nuclear spin baths using a quantum bit, highlighting the creation of dark states as a resource.

Findings

Dark states can be used for coherent control of qubits

Nuclear spin baths can be saturated and manipulated

Dark states serve as long-lived quantum memory

Abstract

We present a unified description of cooling and manipulation of a mesoscopic bath of nuclear spins via coupling to a single quantum system of electronic spin (quantum bit). We show that a bath cooled by the quantum bit rapidly saturates. Although the resulting saturated states of the spin bath (``dark states'') generally have low degrees of polarization and purity, their symmetry properties make them a valuable resource for the coherent manipulation of quantum bits. Specifically, we demonstrate that the dark states of nuclear ensembles can be used to coherently control the system-bath interaction and to provide a robust, long-lived quantum memory for qubit states.