Experimental evaluation of the optimal working temperature for the Josephson threshold detector in single-photon detection applications

The optimal working temperature of Josephson threshold detectors (JTDs) in single-photon detection is a critical factor that directly affects their performance and sensitivity. This study aims to evaluate the optimal working temperature for JTDs to achieve enhanced single-photon detection capabilities. A comprehensive experimental characterization is performed to assess the performance of JTDs over a wide working temperature range, from cryogenic temperatures up to the critical temperature of the Al/AlOx/Al-SIS (superconductor-insulator-superconductor) junction. Additionally, we analyse the underlying physical mechanisms that govern the temperature dependence of JTDs considering the thermal fluctuations, and quasiparticle excitations. Through our evaluation, we identify the optimal working temperature of 39.5 mK (+/- 0.5 mK) out of the working temperature range 35 mK <= T-work <= 45 mK, which optimizes the trade-off between detection efficiency and noise elimination, enabling JTDs to achieve high sensitivity. Furthermore, we estimate various performance metrics of the proposed JTD, such as the detection efficiency, which is estimated to be 0.952, noise equivalent power (NEP) is similar to 3.9 x 10(-18) W.Hz(-1/2), the photon rate is 27.9 photons/s, and signal-to-noise ratio (SNR), which shows a maximum Kumar-Caroll (KC) index value of 97.5 picked 39.5 mK, yielding the best overall performance for the JTDs.