Microwave phase mapping and angle-of-arrival detection using Rydberg atom-based electrometry

We present a method for simultaneously measuring the phase fronts of three or more RF fields using thermal Rydberg atoms. We demonstrate this method using an all-dielectric atomic electrometer acting in a heterodyne configuration to detect three single tone continuous-wave microwave signals propagating in free space. We show that this method can be used to measure the angle of arrival of each source. This method requires no calibration of the incident fields and assumes only far-field distance and phase stability of the incident phase fronts. Because the sensor is minimally perturbing, it provides a direct probe of signal phase even in complex environments, such as the near field of an antenna source or a scattering surface. The measurements presented here are performed using a single scanned sensor, but this technique can trivially be extended to an array of sensors, which would enable phase-sensitive imaging and related applications.