Arbitrary Microwave Polarization Control in a Rydberg Ensemble Experiment

Microwave fields with well-defined polarization are useful for a broad class of experiments such as creating circular Rydberg atoms and tuning of dipole-dipole interactions. However, many cold atom experiments are conducted in steel vacuum chambers, in which producing and measuring well-defined microwave polarization is a challenge. In this work, we demonstrate an approach to generating a microwave field of well-defined arbitrary polarization in a chamber with complicated microwave boundary conditions. Our technique relies on three linearly independent in-vacuum microwave sources with initially unknown polarization, driven with independent phase and amplitude control. After characterizing the field produced by each source using our Rydberg ensemble as a microwave field sensor, we determine the correct linear combination of the three microwave fields that results in the desired final polarization. We demonstrate accurate polarization control both at and away from resonance from Rydberg atomic transitions. The ability to generate arbitrary microwave polarizations at varied frequencies opens the door to microwave control of the interaction of Rydberg atoms.