Heterodyne Sensing of Microwaves with a Quantum Sensor

TL;DR

This paper introduces a heterodyne detection method using diamond quantum sensors that achieves sub-Hz spectral resolution for microwave signals, independent of sensor lifetime, enabling precise sensing over a wide frequency range.

Contribution

The authors demonstrate a heterodyne detection technique with lifetime-independent spectral resolution and control over microwave interactions using dressing fields and Floquet dynamics.

Findings

Achieved spectral resolution below 1 Hz for 4 GHz signals

Demonstrated control of microwave interactions via dressing fields and Floquet dynamics

Enabled high-resolution microwave sensing independent of sensor lifetime

Abstract

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 $1\ \rm{Hz}$ for a $4\ \rm{GHz}$ 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.