High-resolution, Wide-frequency-range Magnetic Spectroscopy with Solid-state Spin Ensembles

Quantum systems composed of solid-state electronic spins can be sensitive detectors of narrowband magnetic fields. A prominent example is the nitrogen-vacancy (NV) center in diamond, which has been employed for magnetic spectroscopy with high spatial and spectral resolution. However, NV-diamond spectroscopy protocols are typically based on dynamical decoupling sequences, which are limited to low-frequency signals (<~20 MHz) due to the technical requirements on microwave (MW) and radio frequency (RF) pulses used to manipulate NV electronic spins. In this work, we experimentally demonstrate an arbitrary frequency magnetic spectroscopy protocol that leverages a quantum frequency mixing (QFM) effect in a dense NV ensemble. We first assess the sensitivity of this protocol across a wide detection frequency range (10 MHz to 4 GHz). By measuring the spectra of multi-frequency test signals near the 0.6, 2.4 and 4 GHz bands, we then demonstrate sub-Hz spectral resolution with a nT-scale noise floor, and precise phase measurement with error <1°. Compared to state-of-the-art NV-diamond techniques for high-resolution magnetic spectroscopy, the QFM protocol significantly extends the detectable frequency range, enabling applications in high-frequency RF and MW signal microscopy and analysis, as well as tesla-scale nuclear magnetic resonance (NMR) spectroscopy and imaging of very small samples at the micron-scale and below.