Production of Circular Rydberg States with Circularly Polarized Microwave Fields

We describe an experimental method of producing circular Rydberg states using a circularly polarized microwave field. A Na $s$ state is excited in the circularly polarized microwave field, and as the field is turned off, it makes an adiabatic rapid passage through a multiphoton resonance and evolves adiabatically into the circular state. Minimal optical selectivity is required and the field can be turned off quickly.