Broadband single microwave photon detector insensitive to thermal noise
Phys. Rev. B 113, 014515 – Published 22 January, 2026
DOI: https://doi.org/10.1103/l46m-rm5y
Abstract
Thermal noise is one of the physical obstacles that constrain the achievable detection sensitivities of various detectors. Indeed, as we showed in a recent paper [Phys. Rev. B 111, 024501 (2025)], the usual Josephson threshold detector (JTD) operated in an equilibrium state can be utilized to implement a weak microwave signal, just approaching (but not arriving at) its energy quantum limit, even though its physical parameters have been optimized. In the present work, we further demonstrate numerically that the phase dynamics of a current-biased Josephson junction can be insensitive to the always-on thermal noise if the sweep rate of the biased current is significantly high. As a consequence, the JTD can be operated alternatively in a nonequilibrium state. Based on the statistical binary detection criterion, we numerically show how such a nonequilibrium JTD (NEJTD) can be utilized to implement the weak microwave signal, theoretically arriving at its energy quantum limit level. The dynamic range and photon-number resolvability of the proposed NEJTD are also discussed numerically, if it can be experimentally realized as a broadband single microwave-photon detector.
