Quantum Mixer to Sense Arbitrary-Frequency Fields

Quantum sensors provide excellent performance combining high sensitivity with spatial resolution. Unfortunately, they can only detect signal fields at frequencies in a few accessible ranges, typically low frequencies up to the experimentally achievable control field amplitudes and a narrow window around their resonance frequencies. Fortunately, arbitrary-frequency signals can be detected by using the sensor qubit as a quantum frequency mixer, enabling a variety of sensing applications. The technique leverages nonlinear effects in periodically driven (Floquet) quantum systems to achieve quantum frequency mixing of the signal and an applied AC bias field. The frequency-mixed field can be detected using Rabi and CPMG sensing techniques with the bias field. Frequency mixing can distinguish vectorial components of an oscillating signal field, thus enabling arbitrary-frequency vector magnetometry. Using this protocol with nitrogen-vacancy centers in diamond to sense a 150 MHz signal field demonstrates the versatility of the quantum mixer sensing technique.