Microwave nanobolometer based on proximity Josephson junctions

Understand

We introduce a microwave bolometer aimed at high-quantum-efficiency detection of wave packet energy within the framework of circuit quantum electrodynamics, the ultimate goal being single microwave photon detection.

• We measure the differential thermal conductance between the detector and its heat bath, obtaining values as low as 5 fW/K at 50 mK.
• This is one tenth of the thermal conductance quantum and corresponds to a theoretical lower bound on noise-equivalent-power of order $10^{-20}$ $W/\sqrt{\mbox{Hz}}$ at 50 mK.
• By measuring the differential thermal conductance of the same bolometer design in qualitatively different environments and materials, we determine that electron--photon coupling dominates the thermalization of our nanobolometer.