An absolute Johnson noise thermometer

TL;DR

This paper presents an absolute Johnson noise thermometer that measures temperature with traceability to fundamental constants, demonstrating high accuracy and potential for improved future precision.

Contribution

The paper introduces a novel Johnson noise thermometer with traceability to fundamental electrical quantities, enabling precise temperature measurements and determination of the Boltzmann constant.

Findings

Measurements agree with standard thermometers within 60 ppm

The device can determine the Boltzmann constant

A pathway for future accuracy improvements is outlined

Abstract

We developed an absolute Johnson noise thermometer (JNT), an instrument to measure the thermodynamic temperature of a sensing resistor, with traceability to voltage, resistance and frequency quantities. The temperature is measured in energy units, and can be converted to SI units (kelvin) with the accepted value of the Boltzmann constant kb; or, conversely, it can be employed to perform measurements at the triple point of water, and obtain a determination of kb. The thermometer is composed of a correlation spectrum analyzer an a calibrated noise source, both constructed around commercial mixed-signal boards. The calibrator generates a pseudorandom noise, by digital synthesis and amplitude scaling with inductive voltage dividers; the signal spectrum is a frequency comb covering the measurement bandwidth. JNT measurements at room temperature are compatible with those of a standard platinum resistance thermometer within the combined uncertainty of 60 ppm. A path towards future improvements of JNT accuracy is also sketched.