Fast and Continuous Detection of Single Microwave Photons via Photo-assisted Quasiparticle Tunneling to a Superconducting Island

We demonstrate a single-photon detector operating in the microwave domain, based on photo-assisted quasiparticle tunneling events that poison a superconducting island. The detection relies on continuously monitoring the island’s charge parity using microwave reflectometry. This scheme achieves 10% detection efficiency with sub 50 ns time resolution and short dead time 1 microsecond, for microwave photons at 10 GHz. The detector features three junctions connected to a superconducting island, which together carry out photoelectric conversion and charge readout. The enhanced light-matter coupling, crucial to photon to quasiparticle conversion, is provided by a granular aluminum-based high-impedance microwave resonator. The time resolved detection of itinerant microwave photon opens up new perspectives in quantum sensing, microwave quantum optics, readout of superconducting qubits and mesoscopic physics.