Researchers at NIST have developed a new method for measuring the Boltzmann constant using electronic noise in resistors. This “noise thermometry” technique is simpler and more compact than previous methods, and could help update the world’s scientific measurement system.
The Boltzmann constant relates energy to temperature for individual particles. The current accepted value is based on a 1988 NIST measurement with an uncertainty of less than 2 parts per million. The new NIST experiment used Johnson noise thermometry to measure the constant with an uncertainty of 12 ppm, consistent with the recommended value.
The international metrology community is expected to soon fix the value of the Boltzmann constant, which would redefine the Kelvin as part of a larger effort to link all units to fundamental constants. This approach would be the most stable and universal way to define measurement units.
The NIST JNT system measures very small electrical noise in resistors when cooled to the water triple point temperature. This “Johnson noise” is created by the random motion of electrons, and the signals they generate are directly proportional to temperature. The electronic devices measuring the noise power are calibrated with electrical signals synthesized by a superconducting voltage source based on fundamental principles of quantum mechanics.
Keywords: Noise, Boltzmann constant, Johnson noise thermometry, Electronic devices, Quantum mechanics
