Microwave Dressed States and Vacuum Fluctuations in a Superconducting Condensate

Abstract

Microwave dressed states are found to emerge within the superconducting condensate when coupled to a quantized electromagnetic field due to photon-Cooper pair entanglement. The renormalized energy separation between these states exceeds the prediction of BCS theory, with the enhancement depending on the number of photons and also arising from electromagnetic vacuum fluctuations. Our work introduces an equilibrium quantum model of microwave-enhanced superconductivity, expanding the theoretical description beyond Eliashberg's non-equilibrium theory. We further demonstrate that the superconducting condensate exerts a back-action on the electromagnetic field, suppressing electric field fluctuations, including those from the vacuum state. This result is consistent with Glauber and Lewenstein's field quantization in dielectric media.