Bolometric detection of Josephson radiation

Abstract: A Josephson junction (JJ) has been under intensive study ever since 1960's. Yet even in the present era of building quantum information processing devices based on many JJs, open questions regarding a single junction remain unsolved, such as quantum phase transitions, coupling of the JJ to an environment and improving coherence of a superconducting qubit. Here we design and build an engineered on-chip reservoir that acts as an efficient bolometer for detecting the Josephson radiation under non-equilibrium (biased) conditions. The bolometer converts ac Josephson current at microwave frequencies, up to about $100\,$GHz, into a measurable dc temperature rise. The present experiment demonstrates an efficient, wide-band, thermal detection scheme of microwave photons and provides a sensitive detector of Josephson dynamics beyond the standard conductance measurements. Using a circuit model, we capture both the current-voltage characteristics and the measured power quantitatively.