Closed cycle 4 K nanowatt meter for hectogram payloads

Superconducting computing research is motivated by fast energy-efficient computing, which creates the challenge of developing components with low-power dissipation requirements. In support of this research, we demonstrate a system that measures heat dissipated by electrical and absorbed optical power in packaged cryogenic devices at a temperature of 4 K. In our system, the device under test resides on a stage that is maintained at a constant 4 K using a feedback heater circuit. The sample stage is cooled via a passive weak thermal link to a stabilized 3 K bath of a closed-cycle pulsed-tube refrigerator. With a maximum device payload of 300 g and a weak thermal link of 13 800 K/W, the empirically determined minimum measurable dissipated power is 300 pW. With a very strong thermal link of 53 K/W, the maximum measurable dissipated power is 30 mW.