Low-Frequency Quantum Sensing

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