All-optical phase-referenced microwave sensing in Rydberg alkali vapors

One of the advantages of Rydberg atom-based detection of microwave and THz fields is weak distortion of the measured field, allowing for precise and stealthy detection. However, recent developments focused on using Rydberg atoms as a RF mixer with a local oscillator field in a superheterodyne-type detection that is no longer all-optical, as the local oscillator antenna has to be a part of the detector. Here we undertake the task of developing an all-optical detection, where the phase reference is provided not in local oscillator, but instead in the polarization of atoms. To realize this feature, we access the 13.9 GHz Rydberg transition in rubidium with two separate optical excitation paths and measure the beating of probe field. We report an overall detection sensitivity of 176 nV/cm/ √Hz and reliable operation up to 3.5 mV/cm of RF field, results that are parallel to superheterodyne detection method demonstrated in the same setup. The results of this work are largely based on an earlier conducted study, published as a preprint.¹ The present manuscript is meant to serve as an appendix to this work, focusing on putting this research in the context of all-optical detection schemes.