Sharp reversals of steady-state nuclear polarisation as a tool for quantum sensing

TL;DR

This paper introduces a quantum sensing method that exploits sharp reversals in nuclear spin polarisation, caused by parameter variations, enabling highly sensitive detection unaffected by electron spin decoherence.

Contribution

It demonstrates that steady-state nuclear polarisation reversals, driven by interference effects, can be used as a robust quantum sensing technique with high frequency resolution.

Findings

Reversals occur with only a few tens of Hz change in Larmor frequency.

Method is robust against electron spin decoherence.

Sensor resolution is not limited by electron coherence time.

Abstract

The polarisation dynamics of nuclear spins weakly coupled to an NV center is highly sensitive to the parameters of the microwave control and the nuclear Larmor frequency. What is commonly regarded as a challenge, we propose here as a resource for quantum sensing. By varying a single experimental parameter in a suitable set-up, i.e., the Rabi frequency of a continual microwave driving or the nuclear Larmor frequency, we predict periodic reversals of the steady-state polarisation of the nuclear spin. Crucially, interference between the transverse and longitudinal dipolar interaction of electron and nuclear spins results in remarkably sharp steady-state polarisation reversals of nuclear spins within only a few tens of Hz change in the nuclear Larmor frequency. Our method is particularly robust against imperfections such as decoherence of the electron spin and the frequency resolution of the sensor is not limited by the coherence time $T_2$ of the electron sensor.