Wideband microwave magnetometry using a nitrogen-vacancy center in diamond

Microwave magnetometry is essential to a variety of modern electronic techniques, most notably integrated circuits. The nitrogen-vacancy center in diamond has shown the ability of nanoscale resolution for the microwave magnetic field measurement and imaging. However, the characterization of the wideband magnetic field remains a challenge. Here we experimentally demonstrated a wideband microwave magnetometry with an off-resonance protocol based on the Bloch-Siegert shift effect. The off-resonance microwave magnetic field shifts the energy level of the nitrogen-vacancy center. It results in a phase accumulation during the evolution of the superposition state of the quantum sensor. According to this effect, by optimizing the evolution time, we experimentally verified the bandwidth widening of an order of magnitude compared with the Rabi oscillation, i.e., on-resonance method with an acceptable decrease of the sensitivity. In addition, we extracted themicrowave frequency with a two-qubit system, which consists of a nitrogen-vacancy center and a nearby C-13 nucleus. This approach enables the building of a wideband and potentially nanoscale microwave magnetometry to allow various potential applications, such as electronic circuits development.