Progress on Johnson noise thermometry using a quantum voltage noise source for calibration

We describe our progress toward a high-precision measurement of temperature using Johnson noise. Using a quantized voltage noise source (QVNS) based on the Josephson effect as a calculable noise source, we have been able to measure the ratio of the gallium and water triple-point temperatures to within an accuracy better than 100 /spl mu/K/K. We also describe the operation of our Johnson noise thermometry system that could be used as a primary thermometer and possible sources of error that limit our absolute temperature measurements to /spl sim/150 /spl mu/K/K.