Photonic heat conduction in Josephson-coupled Bardeen-Cooper-Schrieffer superconductors

TL;DR

This paper studies photon-mediated heat transfer between Josephson-coupled BCS superconductors, finding it negligible compared to galvanic heat flow but significant relative to electron-phonon interactions, with conductance much below the quantum limit.

Contribution

It provides a quantitative analysis of radiative heat transfer in Josephson-coupled BCS superconductors, highlighting its relative insignificance in typical low-temperature experiments.

Findings

Photon-mediated heat flow is negligible compared to galvanic heat flow.

Radiative heat transfer exceeds electron-phonon heat exchange in the studied setup.

Thermal conductance is much smaller than the quantum of thermal conductance.

Abstract

We investigate the photon-mediated heat flow between two Josephson-coupled Bardeen-Cooper-Schrieffer (BCS) superconductors. We demonstrate that in standard low temperature experiments involving temperature-biased superconducting quantum interference devices (SQUIDs), this radiative contribution is negligible if compared to the direct galvanic one, but it largely exceeds the heat exchanged between electrons and the lattice phonons. The corresponding thermal conductance is found to be several orders of magnitude smaller, for real experiments setup parameters, than the universal quantum of thermal conductance, kappa_0(T)=pi k_B^2T/6hbar.