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 using an infrared detector. The lower the NETD, 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 ultra-high sensitivity. We deduced the model for calculating the NETD of a photon-counting-type detector and applied it to our SNSPD-based set-up. Experimentally, we obtained an 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 <1 pW. Furthermore, the intrinsic NETD of this SNSPD is estimated to be <0.1 mK. This work demonstrated a sub-mK temperature resolution when using the SNSPD, paving the way for future remote infrared thermal imaging with high temperature resolution.