Detection of zeptojoule microwave pulses using electrothermal feedback in proximity-induced Josephson junctions

Understand

We experimentally investigate and utilize electrothermal feedback in a microwave nanobolometer based on a normal-metal ($\mbox{Au}_{x}\mbox{Pd}_{1-x}$) nanowire with proximity-induced superconductivity.

• The feedback couples the temperature and the electrical degrees of freedom in the nanowire, which both absorbs the incoming microwave radiation, and transduces the temperature change into a radio-frequency electrical signal.
• We tune the feedback in situ and access both positive and negative feedback regimes with rich nonlinear dynamics.
• In particular, strong positive feedback leads to the emergence of two metastable electron temperature states in the millikelvin range.