Development of 2-K Space Cryocoolers for Cooling the Superconducting Nanowire Single Photon Detector

The superconducting nanowire single photon detector (SNSPD) plays an important role in quantum key distribution, satellite laser ranging, and space quantum communication, etc. The required temperature of around 2K poses a significant challenge for the suitable cryogenic system. Especially, when used in space, the emphasized high reliability, long operation life time, limited room, and power supply make the challenge more formidable. The pulse tube cryocooler (PTC) without any moving component at the cold end has the intrinsic merits of high reliability and long life time at the cold head, and the Stirling-type PTC (SPTC) driven by the linear compressor also achieves the long life time and reliability in the compressor, and thus the SPTC becomes an attractive candidate for cooling the SNSPD. To achieve the aimed 2K, two proposals based on the SPTC are investigated. One is the four-stage SPTC and the other the three-stage SPTC plus a J-T cooler. This paper presents the structural design and performance improvement of both proposals. The measured no-load temperatures of the four-stage SPTC and the three-stage SPTC/J-T are 4.38 and 5.68K, respectively. The final steps to obtain the simulated 2.1- and 1.6K, respectively, are underway.