Low-frequency quantum sensing

TL;DR

This paper introduces a fitting-based quantum sensing algorithm that enables frequency-independent sensitivity for low-frequency fields, demonstrated with nitrogen-vacancy centers achieving high sensitivity below 0.6 kHz.

Contribution

It presents a novel fitting-based method that extends quantum sensing capabilities to low-frequency fields, overcoming limitations of traditional coherence-based techniques.

Findings

Achieved 9.4 nT/Hz^{0.5} sensitivity below 0.6 kHz.

Demonstrated effective measurement of near-constant fields.

Applied the method to real background fields of tens of nTs.

Abstract

Exquisite sensitivities are a prominent advantage of quantum sensors. Ramsey sequences allow precise measurement of direct current fields, while Hahn-echo-like sequences measure alternating current fields. However, the latter are restrained for use with high-frequency fields (above approximately $1$ kHz) due to finite coherence times, leaving less-sensitive noncoherent methods for the low-frequency range. In this paper, we propose to bridge the gap with a fitting-based algorithm with a frequency-independent sensitivity to coherently measure low-frequency fields. As the algorithm benefits from coherence-based measurements, its demonstration with a single nitrogen-vacancy center gives a sensitivity of $9.4$ nT Hz$^{-0.5}$ for frequencies below about $0.6$ kHz down to near-constant fields. To inspect the potential in various scenarios, we apply the algorithm at a background field of tens of nTs, and we measure low-frequency signals via synchronization.