A new high-temperature thermometer

Abhay Shastry, Marcus Rosales, Charles Allen Stafford

Ling Yun Hao, John C. Gallop, J.C. Macfarlane +2 more

A novel form of primary thermometer called the quantum roulette noise thermometer (QRNT), based on flux quantization in a high temperature superconducting (HTS) ring, interrupted by a Josephson junction, has been proposed. The basis of the QRNT is that the flux state of the ring is allowed to evolve freely, and is repeatedly interrogated to establish a probability distribution from which the temperature of the device is derived. Unlike other superconductivity-based noise thermometers, this device is essentially dissipationless, requires no input or output connections, and may be remotely interrogated. The QRNT has the potential to provide high accuracy with short measuring times. Prototype QRNT devices based on thin HTS films have been fabricated and results of initial experimental measurements are presented. Parameters of the experimental devices are compared with predictions of the theoretical model.

Victor Mukherjee, Analía Zwick, Arnab Ghosh +1 more

We consider a thermometer modelled by a dynamically-controlled multilevel quantum system in contact with a bath. Periodic modulation of the energy level spacings of our quantum thermometer enables us to dramatically increase the accuracy of temperature estimation. As opposed to the diverging relative error near the absolute zero obtained in conventional thermometers, our control scheme enables high precision temperature estimation arbitrarily close to the absolute zero, by maximizing its quantum Fisher information. Alternatively, dynamical control may allow for high-precision measurement of multiple temperatures.

Tommy Holmqvist

In this work, normal metal and superconducting tunnel junctions have been studied. In particular applications in low temperature electronic thermometry are investigated. The double oxidation method for achieving high resistance junctions is described and shown to produce high quality devices. A new invention, the single junction thermometer (SJT), is described, and proof of the concept experiments demonstrating the functionality of the device are described. A key feature of the SJT is a well controlled electromagnetic environment surrounding a single junction. It is shown that embedding a single junction within arrays of other junctions is a superior way for controlling the environment as compared to previously proposed methods. Improved thermalisation of electrons is shown to be beneficial for the performance of superconducting RSFQ (Rapid Single Flux Quantum) devices. The so called grey zone of the most basic of these devices, the balanced comparator, is investigated. Improved performance based on metallic cooling fins has been achieved. In the same spirit improved thermalisation of the Coulomb blockade thermometers extends their operation towards lower temperatures. A method employing thick metallic islands was developed and tested to this end.

Sophia Chen