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.

The kelvin, along with the ampere, kilogram, and the mole are likely to\ud be redefined in terms of fundamental constants, in line with Conférence Générale\ud des Poids et Mesures resolution 1 (2011), sometime before 2020. In advance of,\ud and to support, the redefinition, a mise en pratique of the definition of the kelvin\ud (MeP-K) is currently being prepared. The Euramet Metrology Research Programme\ud Implementing the newkelvin (InK) project will coordinate research activity in this field\ud with the objective of improving primary thermometry over the range from 0.0009K\ud to >3000K. Specifically, the project will aim to pursue the following three broad\ud objectives: (1) Support the development of primary thermometry techniques for the\ud realization and dissemination of thermodynamic temperatures, particularly at high\ud (>1300K) and low (<1K) temperatures. This is a major objective of InK because\ud primary thermometry methods at the extremes of temperature should, in principle,\ud have lower uncertainties than defined scales. (2) Determine low uncertainty values\ud of T − T90 in the temperature region where the defined scale is expected to continue\ud providing the lowest uncertainties. This will support the development of theMeP-K and\ud help in the construction of a reliable data set for any possible future temperature scale.\ud (3) Use different thermodynamic thermometry methods to re-determine T − T2000 and therefore hopefully understand the cause of the discrepancy in the background\ud data that constitutes the Provisional Low Temperature Scale of 2000 (PLTS-2000).\ud An overview of the InK project, activities, and intended outcomes is given in this paper

In 1996 the CCT initiated five key comparisons of realisations of the ITS-90 in various parts of the range. CCT-K1 concerns the range 0.65 K to 24.5561 K, where the ITS-90 is defined by specified vapour-pressure equations for 3He (0.65 K to 3.2 K) and 4He (1.25 K to 5.0 K) and by interpolation equations for a constant-volume gas thermometer (3 K to 24.5561 K). The transfer standards were rhodium–iron resistance thermometers calibrated by the seven participating laboratories. The report describes the comparison experiments, the results and uncertainties, and the calculation of interlaboratory equivalences. The comparison has been concluded by preparing an entry for Appendix B of the BIPM Key Comparison Database.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

The operation of the primary Coulomb blockade thermometer (CBT) is based on a measurement of bias voltage dependent conductance of arrays of tunnel junctions between normal metal electrodes. Here we report on a comparison of a CBT with a high accuracy realization of the PLTS-2000 temperature scale in the range from 0.008 K to 0.65 K. An overall agreement of about 1% was found for temperatures above 0.25 K. For lower temperatures increasing differences are caused by thermalization problems which are accounted for by numerical calculations based on electron-phonon decoupling.

The application of a magnetic-field-fluctuation thermometer (MFFT) is described for practical thermometry in the low-temperature range. The MFFT inductively measures the magnetic noise generated by Johnson noise currents in a metallic temperature sensor. The temperature of the sensor is deduced from its thermal magnetic noise spectrum by applying the Nyquist theorem, making the thermometer in principle linear over a wide range of temperatures. In this setup, a niobium-based dc SQUID gradiometer detects the magnetic field fluctuations. The gradiometer design optimizes the inductive coupling to the metallic temperature sensor, yet equally ensures sufficient insensitivity to external magnetic interference. In order to obtain a highly sensitive and fast thermometer, the SQUID chip is placed directly onto the surface of the temperature sensor. The compact setup of the gradiometer/temperature sensor unit ensures good conditions for thermal equilibration of the sensor with the temperature to be measured, a factor that becomes increasingly important in the temperature range below 1 K. The first direct comparison measurements of the MFFT with a high-accuracy realization of the Provisional Low Temperature Scale of 2000 (PLTS-2000) are presented. Special emphasis is given to the investigation of the linearity, speed, and accuracy of the MFFT.