Proposed cavity Josephson plasmonics with complex-oxide heterostructures

We discuss how complex-oxideheterostructures that include high-${T}_{c}$ superconducting cupratescan be used to realize an array of submillimeter cavities that support Josephson plasmon polaritons. These cavities have several attractive features for new types of light-matter interaction studies and we show that they promote ``ultrastrong'' coupling between THz frequency radiation and Josephson plasmons. Cavity electrodynamics of Josephson plasmonsallows us to manipulate the superconducting order-parameter phase coherence. As an example, we discuss how it could be used to cool superconducting phase fluctuations with light.