Diamond quantum sensors are sensitive to weak microwave magnetic fields resonant to the spin transitions. However the spectral resolution in such protocols is limited ultimately by sensor lifetime. Here we demonstrate a heterodyne detection method for microwaves (MW) leading to a lifetime independent spectral resolution in the GHz range. We reference the MW-signal to a local oscillator by generating the initial superposition state from a coherent source. Experimentally we achieve a spectral resolution below 1Hz for a 4GHz signal far below the sensor lifetime limit of kilohertz. Furthermore we show control over the interaction of the MW-field with the two level system by applying dressing fields, pulsed Mollow absorption and Floquet dynamics under strong longitudinal radio frequency drive. While pulsed Mollow absorption leads to highest sensitivity, the Floquet dynamics allows robust control independent from the systems resonance frequency. Our work is important for future studies in sensing weak microwave signals in wide frequency range with high spectral resolution.
@article{arxiv.2008.10068,
title = {Heterodyne Sensing of Microwaves with a Quantum Sensor},
author = {Jonas Meinel and Vadim Vorobyov and Boris Yavkin and Durga Dasari and Hitoshi Sumiya and Shinobu Onoda and Junichi Isoya and Jörg Wrachtrup},
journal= {arXiv preprint arXiv:2008.10068},
year = {2021}
}