Sub-millikelvin-resolved superconducting nanowire single-photon detector operates with sub-pW infrared radiation power

The noise equivalent temperature difference (NETD) indicates the minimum temperature difference resolvable by an infrared detector. The lower the NETD is, the better the sensor can register small temperature differences. In this work, we proposed a strategy to achieve a high temperature resolution using a superconducting nanowire single-photon detector (SNSPD) with ultrahigh sensitivity. We deduced the model for calculating the NETD of a photon-counting type detector and applied it to our SNSPD-based setup. Experimentally, we obtained a NETD as low as 0.65 mK, which is limited by the background radiation of the environment, and the required infrared radiation power is calculated to be less than 1 pW. Furthermore, the intrinsic NETD of this SNSPD is estimated to be less than 0.1 mK. This work demonstrated a sub-mK temperature resolution with the SNSPD, paving the way for future remote infrared thermal imaging with high temperature resolution.