Interplay between Cavity Quantum Electrodynamics and Superconductivity

There is currently much interest in studying solids placed in optical cavities to uncover new phases and phenomena in the complete absence of any external fields other than the fluctuating vacuum, or zero-point, electromagnetic fields. Judicious engineering of the quantum vacuum surrounding the matter inside the cavity can lead to nonintuitive modifications of electronic states and novel properties. Here we study superconducting films inside terahertz cavities in search of some of the recently predicted phenomena due to a redistribution of Bogoliubov quasiparticles as well as the formation of novel superconductor-cavity-polaritons. We measured the transition temperatures of both Bardeen-Cooper-Schrieffer (BCS) and non-BCS superconducting thin films of various thicknesses inside a cavity by temperature-dependent electrical resistivity measurements. We also performed terahertz time-domain spectroscopy measurements to study the influence of cavity fields on the optical conductivity spectra of the films. The obtained results will be analyzed using existing theoretical models, and future steps for uncovering new phenomena in the superconductor cavity light–matter coupled system will be discussed.