Cooling photon-pressure circuits into the quantum regime

TL;DR

This paper demonstrates the cooling of a radio frequency circuit into the quantum regime using superconducting circuits and photon-pressure interaction, enabling RF quantum photonics at cryogenic temperatures.

Contribution

It introduces a method to achieve quantum ground state cooling of RF circuits via enhanced photon-pressure coupling in superconducting LC circuits.

Findings

75% reduction in thermal RF occupancy with less than one pump photon

Coupling rate exceeds RF thermal decoherence rate by a factor of 3 at higher powers

Large single-photon quantum cooperativity $ ext{~}1$ achieved

Abstract

Quantum control of electromagnetic fields was initially established in the optical domain and has been advanced to lower frequencies in the gigahertz range during the past decades extending quantum photonics to broader frequency regimes. In standard cryogenic systems, however, thermal decoherence prevents access to the quantum regime for photon frequencies below the gigahertz domain. Here, we engineer two superconducting LC circuits coupled by a photon-pressure interaction and demonstrate sideband cooling of a hot radio frequency (RF) circuit using a microwave cavity. Because of a substantially increased coupling strength, we obtain a large single-photon quantum cooperativity $\mathcal{C}_{\mathrm{q}0} \sim 1$ and reduce the thermal RF occupancy by 75% with less than one pump photon. For larger pump powers, the coupling rate exceeds the RF thermal decoherence rate by a factor of 3, and the RF circuit is cooled into the quantum ground state. Our results lay the foundation for RF quantum photonics.