A Magnetic-Field-Fluctuation Thermometer for the mK Range Based on SQUID-Magnetometry

Abstract

We are developing a compact and easy-to-use thermometer for the temperature range of about 10 mK to 4 K based on the measurement of magnetic noise above the surface of a metal body which acts as a temperature sensor. The metal body is thermally anchored to the temperature to be measured. The magnetic field fluctuations arise from the thermally agitated motion of electric charges and can be related to the temperature of the metal via Nyquist's relation of the noise in a conductor. We measure the magnetic field fluctuations with a highly sensitive low-Tc dc SQUID magnetometer which is at the same temperature stage as the metal body and in close vicinity to the metal surface. The temperature to be measured is extracted from the spectrum of thermal magnetic noise detected by the magnetometer. The SQUID magnetometer used is a miniature multiloop magnetometer with maximized field sensitivity and low power dissipation. The spectrum of thermal magnetic noise detected by the magnetometer is significantly affected by the configuration of the metal sensor and the magnetometer. We discuss considerations regarding the configuration of an integrated magnetic-field-fluctuation thermometer and present measurements of its sensitivity and speed.

Magnetic cooling for microkelvin nanoelectronics on a cryofree platform

“…The temperature is measured using an inductive Johnson noise thermometer [12][13][14] , which operates over a broad range of temperatures from 4 K down to 150 µK. The noise thermometer is an ideal choice for low temperature applications, because self-heating is reduced due to the inductive readout and the thermometer has the potential to reach the low µK-regime.…”

A New Generation of Primary Luminescent Thermometers Based on Silicon Nanoparticles and Operating in Different Media

“…Regarding the calibration process, the thermometric systems can be classified in two categories: (i) primary or semi‐primary thermometers that are characterized by well‐established equations of state, directly relating the measured parameter to temperature, or (ii) secondary thermometers that require calibration . While for non‐self‐calibrated secondary thermometers, the calibration curve must be determined prior to each measurement, for self‐calibrated secondary thermometers, the calibration curve is obtained by fitting the thermometric parameter values measured in a given temperature range to an arbitrary function .…”

Low-temperature thermometry below 1 K at PTB

“…During the last years the development of noise thermometers at PTB has focused on dc superconducting quantum interference device (SQUID) based low-temperature noise thermometers as magnetic field fluctuation thermometers (MFFT) [9] and current sensing noise thermometers (CSNT) [10]. In both variants the temperature sensor is a metallic resistor.…”