Stroboscopic detection of itinerant microwave photons

Abstract

We present a scheme to detect itinerant microwave radiation at the single photon level. Using existing Josephson-photonics devices, where two microwave cavities are coupled by a dc-voltage-biased superconducting junction, we theoretically show how to implement a stroboscopically repeated, near-projective measurement of a photon impinging on one of the cavities. Optimizing rate, duration, and strength of the measurement by flux control of the junction and developing a threshold protocol to detect the photon from a homodyne measurement of the radiation output of the other cavity, we achieve highly efficient detection with low dark counts. By cascading the detector with a preamplifier, where a similar two-cavity Josephson-photonics device acts as a photon multiplier, we can further improve the device to reach a detection efficiency of 88.5% with a dark count rate of ~10-4⁢ gamma_a, set by the resonance width gamma_a of the absorbing cavity. These results for a preamplification factor of 2 suggest that higher preamplification factors may yield near-unity efficiencies.