Current-sensing noise thermometry from 4.2 K to below 1 mK using a DC SQUID preamplifier

2003 
Abstract We are using a low- T c DC SQUID to perform current-sensing noise thermometry, by measuring the thermal noise currents in a copper resistor. The temperature is obtained from the Nyquist formula. This is a practical thermometer for use from 4.2 K to below 1 mK , with a percentage precision independent of temperature. Using a 0.34 mΩ resistor, the thermometer had an amplifier noise temperature T N of 8 μK . A precision of 1.5% was obtained in 200 s . The thermometer was in good agreement with the PLTS-2000 3 He melting curve scale down to 4.5 mK . We have cooled the thermometer successfully below 1 mK , achieving a minimum electron temperature of 300 μK .
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