  We address, using concepts of the microscopic theory of superconductivity,
parametric amplifiers and kinetic inductance detectors focusing on the
interaction of microwave radiation with the superconducting condensate. This
interaction was identified recently as the source of the apparent dissipation
in microwave superconducting micro-resonators at low temperatures. Since the
evaluation of the performance of practical devices based only on the
microwave-response is not sufficiently informative about the underlying
physical processes, we propose an experimental system to measure the
microscopically relevant spectral functions as well as the non-equilibrium
distribution function of a microwave-driven superconducting wire. The results
indicate the limits of the commonly used phenomenological theories, providing
the groundwork for further optimisation of the performance.

Superconductivity