NIST has significantly improved its Johnson-noise thermometry system, which is crucial for determining the value of the Boltzmann constant (k) as part of the upcoming redefinition of the International System of Units (SI) in 2018. The upgraded system can measure k with a statistical uncertainty of 12 parts per million, making it a valuable tool for comparing values obtained through different physics and technologies.
The key innovation enabling this improvement is the Quantized Voltage Noise Source (QVNS), developed at NIST’s Boulder laboratories. The QVNS generates a precisely controllable amount of voltage fluctuation equivalent to thermal voltage noise, using arrays of Josephson junctions that operate with quantum accuracy. This allows NIST’s JNT instruments to operate in either absolute or relative measurement modes, providing greater flexibility and functionality compared to conventional JNT methods.
NIST’s JNT research is conducted at three locations on its Maryland and Colorado campuses, and is the only experiment in the world measuring the ratio of k to h. This approach makes the measurement of k more accurate because of the much lower uncertainty in the value of h. The improved electronics suite helps minimize errors in the amplification and matching of the signals.
The International Temperature Scale of 1990 and companion documents specify numerous fixed reference points, and one important function of the JNT is to provide absolute primary thermometer measurements for several of these fixed points in the international temperature scale.
Source: https://www.nist.gov/news-events/news/2016/11/noise-temperature-and-new-si
Keywords: Enabling Technologies and Quantum Devices, Quantum Sensing and Metrology
