Exploiting ionization dynamics in the nitrogen vacancy center for rapid, high-contrast spin and charge state initialization

TL;DR

This paper introduces a novel method leveraging ionization dynamics in NV centers to enhance spin measurement sensitivity, achieving significant contrast improvements and faster measurement speeds in quantum sensing applications.

Contribution

The authors experimentally demonstrate a two-step protocol that increases spin contrast and reduces initialization errors in NV centers, improving quantum sensing performance.

Findings

Contrast improved by 17% using the protocol.

Initialization error reduced by over 50%.

Measurement speed increased by more than 1.5 times for long sequences.

Abstract

We propose and experimentally demonstrate a method to strongly increase the sensitivity of spin measurements on nitrogen-vacancy (NV) centers in diamond, which can be readily implemented in existing quantum sensing experiments. While charge state transitions of this defect are generally considered a parasitic effect to be avoided, we show here that these can be used to significantly increase the NV center's spin contrast, a key quantity for high sensitivity magnetometry and high fidelity state readout. The protocol consists of a two-step procedure, in which the charge state of the defect is first purified by a strong laser pulse, followed by weak illumination to obtain high spin polarization. We observe a relative improvement of the readout contrast by 17 %, and infer a reduction of the initialization error of more than 50 %. The contrast enhancement is accompanied by a beneficial increase of the readout signal. For long sequence durations, typically encountered in high-resolution magnetometry, a measurement speedup by a factor of >1.5 is extracted, and we find that the technique is beneficial for sequences of any duration. Additionally, our findings give detailed insight into the charge and spin polarization dynamics of the NV center, and provide actionable insights for direct optical, spin-to-charge, and electrical readout of solid-state spin centres.