2026/03/17 by Hanna Zeller, Lukas Danner, Max Hofheinz +3
Physics and Astronomy · #quant-ph #cond-mat.mes-hall #cond-mat.supr-con
paper · pdf · doi:10.1103/xnm9-98cm
published as Phys. Rev. Research 8, 033145 (2026) · 13 pages, 12 figures
arxiv created 2026/03/17 · arxiv updated 2026/08/07
We present a novel 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 γa, set by the resonance width γa of the absorbing cavity. These results for a multiplication factor of two suggest that near-unity efficiencies may be reached for higher multiplication factors.