Robert McDermott, Physics Department, University of Wisconsin/Madison

Topic: "Microwave Photon Counter Based on Josephson Junctions"  (Video)

Abstract: The strong interaction of superconducting integrated circuits with microwave photons forms the basis of circuit quantum electrodynamics (cQED), an attractive paradigm for scalable quantum computing and a test bed for quantum optics in the strong coupling regime . Most quantum optics protocols rely on photon counters to probe the state of the light field. While optical photon counters are well established, the detection of single microwave photons is exceedingly difficult, due to the small energy of the photon. In this talk I describe a microwave photon counter based on a current-biased Josephson junction. The absorption of a single microwave photon causes the junction to transition to the voltage state, producing a large and easily measured classical signal. With a two-junction circuit, we have performed a microwave version of the Hanbury Brown and Twiss experiment, and demonstrated a clear signature of microwave photon bunching for a thermal source. The design is readily scalable to tens of parallelized junctions, a configuration that would allow number-resolved counting of microwave photons.