Overcoming frequency resolution limits using a solid-state spin quantum sensor
Qingyun Cao, Genko T. Genov, Yaoming Chu, Jianming Cai, Yu Liu, Alex Retzker, Fedor Jelezko, arXiv：2506.20416 (2025)
The ability to determine precisely the separation of two frequencies is fundamental to spectroscopy, yet the resolution limit poses a critical challenge: distinguishing two incoherent signals becomes impossible when their frequencies are sufficiently close. Here, we demonstrate a simple and powerful approach, dubbed superresolution quantum sensing, which experimentally resolves two nearly identical incoherent signals using a solid-state spin quantum sensor. By identifying a sequence of ``magic interrogation times'', we eliminate quantum projection noise, overcoming the vanishing distinguishability of signals with near-identical frequencies. This leads to improved resolution, which scales as t-2 in comparison to the standard t-1 scaling. Together with a greatly reduced classical readout noise assisted by a nuclear spin, we are able to achieve sub-kHz resolution with a signal detection time of 80 microseconds. Our results highlight the potential of quantum sensing to overcome conventional frequency resolution limitations, with broad implications for precision measurements.