Quantum sensing with arbitrary frequency resolution via correlation measurements

Achieving high frequency spectral resolution with quantum sensors is crucial in fields ranging from physical to biological sciences but it remains challenging. Synchronized readout techniques have been introduced to achieve this goal with Nitrogen-Vacancy centers in diamond, but they require long measurement times T for a ~1/T frequency resolution, and suffer from signal reduction due to higher harmonics, requiring prior knowledge to avoid this limitation. Here, we introduce a novel protocol that achieves high frequency resolution by measuring phase correlations of AC magnetic fields using ensembles of NV centers. Our method extends the sensing bandwidth to frequencies higher than the system’s Rabi frequency while achieving arbitrary frequency resolution, limited only by the target field’s coherence time. Moreover, our approach does not degrade as the target field amplitude increases, extending its dynamic range or allowing the application of more decoupling π-pulses, which in turns make the sensor more robust to higher-frequency noise. Indeed, the higher harmonics present in the acquired signal contribute constructively to the measured correlations, ultimately improving the frequency resolution per unit time to ~1/nBT, where n is the number of π-pulses in the dynamical decoupling sequence and B is the AC magnetic field strength. Our method paves the way for achieving arbitrary frequency resolution with improved performance, making it highly versatile for quantum sensing applications across diverse scientific fields.