A hybrid apparatus for coupling single mm-wave and optical photons using Rydberg atoms

We present a hybrid experiment which employs Rydberg atoms to couple single optical and mm-wave photons. The centerpiece of the setup is a superconducting mm-wave cavity that intersects with an optical resonator while providing optical access to cool and trap atoms. Strong electric dipole coupling between Rydberg states, along with high cavity quality factors of up to 10⁷ at 100 GHz and 1 K, enables exceptionally high single-atom cooperativity values in the system. Here, we share our observation of Rydberg electromagnetically induced transparency (EIT) in the hybrid cavity with a mm-wave quality factor of 200,000 at 5 K. We further demonstrate the platform’s capabilities by tuning an atomic resonance to a mm-wave cavity mode using an auxiliary mm-wave field, and showing Autler-Townes splitting of the EIT by the resonant mm-wave mode. We also describe our efforts to increase the coherence times of Rydberg states to enable operation in the strong coupling limit. Finally, we discuss our progress towards realizing a high-efficiency and high-bandwidth mm-wave-optical quantum transducer using this platform.