Towards superconducting mmwave cavity-induced spin squeezing in a neutral cold atom ensemble

Using a cavity to enhance interactions between light and neutral atoms has been investigated for two decades. Its cooperativity, the quantity characterizing the quantum-level interaction strength compared with the decoherence process, however, is surpassed by and is now at least six orders of magnitude behind the superconducting circuit counterparts. Here, we report our recent progress in merging the highly developed superconducting technique and the advantageous properties of neutral atoms, like homogeneity and long coherence time. Specifically, we dress an ensemble of cold Rb atoms by the Rydberg level, which strongly interacts with a superconducting mmwave cavity, to engineer the collective spin state. We showcase this platform by generating spin squeezing, which can be generalized to many highly non-classical states such as the GHZ state, enabled by the strong and unitary interaction offered by the superconducting mmwave cavity and Rydberg levels of neutral Rb atoms.