Strong coupling and active cooling in a hybrid atom-cavity system at finite temperature*

Hybrid quantum computation exploits the unique strengths of disparate quantum technologies, enabling realization of a scalable quantum device capable of both fast gates and long coherence times. Neutral atoms provide an attractive candidate for interfacing with superconducting microwaves resonators due to the long lifetimes of Rydberg states at low temperatures and strong coupling of the large electric dipole moment to the cavity field. This provides a route to achieving efficient optical to microwave conversion and enabling long-lived neutral atom quantum memories, as well as enabling future integration with fast superconducting microwave qubits.

We demonstrate that using a hybrid system of a superconducting cavity coupled to a multi-level Rydberg atom it is possible to observe the quantum nature of strong coupling even at finite temperatures where the thermal occupation of microwave mode cannot be neglected [1]. We exploit this coupling to permit cooling of the thermal microwave mode towards the ground-state, enabling observation of coherent vacuum Rabi oscillations even at 4 K for realistic experimental parameters, circumventing requirements for integration in a dilution refrigerator. Cooling using multiple atoms is also explored, showing maximal cooling for small samples making this a viable approach to cavity cooling with potential applications in long-range coupling of superconducting circuits via thermal waveguides.

[1] Keary, L. F. & Pritchard, J. D. Strong coupling and active cooling in a finite temperature hybrid atom-cavity system. Preprint at https://arxiv.org/abs/2108.01386 (2021).