Millikelvin Temperatures Measured with a Noise Thermometer: Brownian motion in electrical circuits has been used to measure temperatures as low as 2 millikelvins.

We find that the current-sensitive noise thermometer is a satisfactory sensor of absolute temperature down to 2 mK and possibly below. Its field of application is primarily to magnetically and electrically quiet situations where accuracy is important and high precision is not required. For example the noise thermometer is an ideal instrument for calibrating a secondary thermometer, such as a pressure thermometer, whose calibration can readily and accurately be transferred from one laboratory to another. Further instrumental development for millidegree applications seems unnecessary at present. Rather the major problems in millikelvin noise thermometry that require attention in the immediate future involve establishing thermal contact to the thermometer and reducing its thermal response time.