# Protecting a diamond quantum memory by charge state control

## TL;DR

This paper demonstrates how controlling the charge state of NV centers in diamond can significantly extend nuclear spin coherence times and enable individual optical addressability, advancing solid-state quantum memory technology.

## Contribution

It identifies and characterizes the positively charged NV center as a new charge state for improved quantum memory performance and control.

## Key findings

- Nuclear spin coherence times increased by a factor of 20.
- Charge state control enables individual optical addressability.
- Positively charged NV center is electron-spin-less and optically inactive.

## Abstract

In recent years, solid-state spin systems have emerged as promising candidates for quantum information processing (QIP). Prominent examples are the Nitrogen-Vacancy (NV) center in diamond, phosphorous dopants in silicon (Si:P), rare-earth ions in solids and V$_{\text{Si}}$-centers in Silicon-carbide (SiC). The Si:P system has demonstrated, that by eliminating the electron spin of the dopant, its nuclear spins can yield exceedingly long spin coherence times. For NV centers, however, a proper charge state for storage of nuclear spin qubit coherence has not been identified yet. Here, we identify and characterize the positively charged NV center as an electron-spin-less and optically inactive state by utilizing the nuclear spin qubit as a probe. We control the electronic charge and spin utilizing nanometer scale gate electrodes. We achieve a lengthening of the nuclear spin coherence times by a factor of 20. Surprisingly, the new charge state allows switching the optical response of single nodes facilitating full individual addressability.