Current Sensing Noise Thermometer Research Articles

Precise Calorimetry of Small Metal Samples Using Noise Thermometry

AbstractWe describe a compact calorimeter that opens ultra-low-temperature heat capacity studies of small metal crystals in moderate magnetic fields. The performance is demonstrated on the canonical heavy fermion metal YbRh$$_{2}$$ 2 Si$$_{2}$$ 2 . Thermometry is provided by a fast current sensing noise thermometer. This single thermometer enables us to cover a wide temperature range of interest from 175 µK to 90 mK with temperature-independent relative precision. Temperatures are tied to the international temperature scale with a single-point calibration. A superconducting solenoid surrounding the cell provides the sample field for tuning its properties and operates a superconducting heat switch. Both adiabatic and relaxation calorimetry techniques, as well as magnetic field sweeps, are employed. The design of the calorimeter results in an addendum heat capacity which is negligible for the study reported. The keys to sample and thermometer thermalisation are the lack of dissipation in the temperature measurement and the steps taken to reduce the parasitic heat leak into the cell to the tens of fW level.

New Evaluation of $$T-T_{2000}$$ T - T 2000 from 0.02 K to 1 K by Independent Thermodynamic Methods

This paper reports on the results achieved within the European Metrology Research Programme project “Implementing the new kelvin—InK” in the low-temperature range below 1 K. One of the main objectives of the InK project was the determination of new thermodynamic temperature data for comparison with the Provisional Low Temperature Scale 2000 (PLTS-2000), to provide reliable $$T-T_{2000}$$ values. To this end, we have investigated three different types of primary thermometers: the current sensing noise thermometer, the primary magnetic field fluctuation thermometer and the Coulomb blockade thermometer. Based on a thorough investigation of the thermometers, detailed uncertainty budgets were established for the measurement of thermodynamic temperatures. Direct comparison measurements between all thermometers demonstrate the agreement of temperature measurements within less than 1 %. Our new $$T-T_{2000}$$ data confirm the correctness of the PLTS-2000 in the temperature range from 20 mK up to about 700 mK with relative combined standard uncertainties better than 0.62 %.

Primary current-sensing noise thermometry in the millikelvin regime.

The use of low-temperature platforms with base temperatures below 1 K is rapidly expanding, for fundamental science, sensitive instrumentation and new technologies of potentially significant commercial impact. Precise measurement of the thermodynamic temperature of these low-temperature platforms is crucial for their operation. In this paper, we describe a practical and user-friendly primary current-sensing noise thermometer (CSNT) for reliable and traceable thermometry and the dissemination of the new kelvin in this temperature regime. Design considerations of the thermometer are discussed, including the optimization of a thermometer for the temperature range to be measured, noise sources and thermalization. We show the procedure taken to make the thermometer primary and contributions to the uncertainty budget. With standard laboratory instrumentation, a relative uncertainty of 1.53% is obtainable. Initial comparison measurements between a primary CSNT and a superconducting reference device traceable to the PLTS-2000 (Provisional Low Temperature Scale of 2000) are presented between 66 and 208 mK, showing good agreement within the k=1 calculated uncertainty.

A microkelvin cryogen-free experimental platform with integrated noise thermometry

We report experimental demonstration of the feasibility of reaching temperatures below 1 mK using cryogen-free technology. Our prototype system comprises an adiabatic nuclear demagnetization stage, based on hyperfine-enhanced nuclear magnetic cooling, integrated with a commercial cryogen-free dilution refrigerator and 8 T superconducting magnet. Thermometry was provided by a current-sensing noise thermometer. The minimum temperature achieved at the experimental platform was 600 μK. The platform remained below 1 mK for over 24 h, indicating a total residual heat-leak into the experimental stage of 5 nW. We discuss straightforward improvements to the design of the current prototype that are expected to lead to enhanced performance. This opens the way to widening the accessibility of temperatures in the microkelvin regime, of potential importance in the application of strongly correlated electron states in nanodevices to quantum computing.

Focus on vacuum and cryogenics

Focus on vacuum and cryogenics

An Ultra High Sensitive Current Sensor based on Superconducting Quantum Interference Device

The developed sensor design is based on a suitable superconducting intermediary (matching) magnetic flux transformer magnetically coupled to a niobium based dc-SQUID (Superconducting Quantum Interference Device). The 60 square niobium turns (20 μm width) signal coil is tightly coupled to the matching transformer consisting of a square single turn primary coil connected in series with a multiturn secondary coil. The obtained signal current to magnetic flux transfer factor (current sensitivity) is equal to 62 nA/Φ0 measured by using a current sensing noise thermometer technique. The sensor has been characterized in liquid helium by using a direct coupling low noise readout electronic and the flux locked loop configuration. Despite the circuit complexity, the sensor has exhibited a smooth and free resonance voltage-flux characteristic ensuring a stable working operation. Considering a SQUID magnetic flux noise √SΦ = 1.8 μΦ0/√Hz at T = 4.2 K, a current noise as low as 110 fA/√Hz is obtained. Due to his high performance such sensor can be employed in all application requiring an extremely current sensitivity, like the readout of the gravitational wave detectors and the current sensing noise thermometry.

An ultralow noise current amplifier based on superconducting quantum interference device for high sensitivity applications

An integrated ultrahigh sensitive current amplifier based on a niobium dc superconducting quantum interference device (SQUID) has been developed. The sensor design is based on a multiturn signal coil coupled to a suitable SQUID magnetometer. The signal coil consists of 60 square niobium turns tightly coupled to a superconducting flux transformer of a SQUID magnetometer. The primary coil (pick-up coil) of the flux transformer has been suitably designed in order to accommodate the multiturn input coil. It has a side length of 10 mm and a width of 2.4 mm. In such a way we have obtained a signal current to magnetic flux transfer coefficient (current sensitivity) as low as 62 nA∕Φ(0). The sensor has been characterized in liquid helium by using a direct coupling low noise readout electronic and a standard modulated electronic in flux locked loop configuration for the noise measurements. Beside the circuit complexity, the sensor has exhibited a smooth and free resonance voltage-flux characteristic guaranteeing a reliable and a stable working operation. Considering a SQUID magnetic flux noise of S(Φ)(1∕2) = 1.8 μΦ(0)∕Hz(1∕2) at T = 4.2 K, a current noise as low as 110 fA∕Hz(1∕2) is obtained. Such a value is about a factor two less than the noise of other SQUIDs of the same category. As an application, Nyquist noise measurements of integrated test resistors using the current sensing noise thermometer technique are reported. Due to its high performance such a sensor can be employed in all applications requiring an extremely current sensitivity like the readout of the gravitational wave detectors and the current sensing noise thermometry.

Practical noise thermometers for low temperatures

Thermometry over broader temperature ranges below 4 K usually requires the application of different thermometers to have sufficient precision and accuracy. We have developed dc SQUID-based noise thermometers which cover the temperature range from 4 K to below 10 mK. The working principle is based on the detection of thermal magnetic flux noise generated by noise currents in a metallic temperature sensor. The noise thermometers exhibit a linear characteristic via the Nyquist relation, are fast, compact, and easy to use. The current sensing noise thermometer and the magnetic field fluctuation thermometer we present can be designed to meet different requirements concerning speed and accuracy of the temperature measurement. In both variants the temperature sensor and the SQUID are located at the same temperature level. Experimental results will be given for the characteristics of the thermometers as well as for comparison measurements with the PLTS-2000. A commercial noise thermometer version now is available through the company MAGNICON.

EU dissemination of the provisional ultra-low-temperature scale, PLTS-2000

Following the introduction of the provisional low-temperature scale from 0.9 mK to 1K, PLTS-2000, there is a need for primary and secondary thermometers and fixed points, which can disseminate the scale to users. This paper reports on the progress, within the EU collaborative project ‘ULT Dissemination’, in the development and evaluation of several devices with associated instrumentation. Principal among them are a current-sensing noise thermometer, a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound thermometer, a 3 He melting pressure thermometer for a direct realisation of the PLTS-2000. A superconductive reference device has also been developed, as a replacement for the NBS SRM-768 which is no longer available.

Current sensing noise thermometry for millikelvin temperatures using a DC SQUID preamplifier

We have demonstrated the performance of a current sensing noise thermometer using a low- T c DC SQUID as the front end amplifier. The thermometer is fast, absolute and precise and is usable over a wide temperature range below 4.2 K, in principle down to below 1 mK. We have shown that it is possible to determine absolute temperature with a precision of 1% in a measuring time of 10 sec with a noise temperature of ∼30 μK , and to an accuracy of better than 0.3%. The percentage precision is independent of temperature. A comparison with the 3He melting curve down to 24 mK is reported.