Photonic heat transport across a Josephson junction

We present a detailed study of photonic heat transport across a Josephson junction coupled to two arbitrary linear circuits having different temperatures. First, we consider the linear approximation, in which a nonlinear Josephson potential is replaced by a quadratic one and the junction acts as an inductor. Afterwards, we discuss the effects of junction anharmonicity. We separately consider the weak-coupling limit, in which the Bloch band structure of the junction energy spectrum plays an important role, and the opposite strong-coupling regime. We apply our general results to two specific models: a Josephson junction coupled to two Ohmic resistors and two resonators. We derive simple analytical approximations for the photonic heat flux in many limiting cases. We demonstrate that electric circuits with embedded Josephson junctions provide a useful platform for quantum thermodynamics experiments.