Ultralow temperature Josephson primary thermometry

Abstract

We are developing a primary thermometer for operation from 4.2 K down to millikelvin temperatures. The principle of the thermometer is to measure thermal fluctuations in a thin-film resistor by transducing them into phase fluctuations in a Josephson junction. These fluctuations are then inductively coupled to a DC SQUID preamplifier. All elements are fabricated on a single integrated circuit chip in niobium technology using Ti/Pd/Au as shunt resistors and the thermometric device. Our SQUIDs are fully operational down to millikelvin temperatures.