Boltzmann Constant Measurements Using QVNS-Based Johnson Noise Thermometry at NMIJ, AIST

Abstract

Among various methodologies of thermodynamic temperature measurements, Johnson noise thermometry (JNT) has an advantage that the structure and size of the temperature sensing probe are similar to conventional probes for contact thermometry. Another distinguishing feature is that the measurements are all electronic. Furthermore, the application of a quantum voltage noise source (QVNS), first introduced by the National Institute of Standards and Technology (NIST), has improved the accuracy of JNT during the past ten years. These developments have been driven under the rationale to determine the Boltzmann constant $$k$$ , in support of the proposed redefinition of the kelvin, and later to provide practical realization of the kelvin. At NMIJ, AIST, we have been developing a QVNS-based JNT system to first measure the Boltzmann constant and then aim to extend the temperature range to higher temperatures where $$T-T_{90}$$ data are lacking. An impact feature of our system is that most of our key elements have been built independently from NIST and the National Institute of Metrology, China (NIM); in particular that the Josephson junction array has been built in house at NeRI, AIST, and its driving method differs from that of either NIST or NIM. In this paper, the unique elements of the system as well as our initial results on the Boltzmann constant measurements are reported.