ULT Engineering and Technology

The impact of this development is on manufacturing– in the leading cryogenics industry in the UK, and on metrology—in the international definition of the unit of temperature (Kelvin), and on commercial quantum computing—the primary market for ultra-low temperatures.

The principle strands of our research are:

• Cryogen-free ultralow temperature platforms
• Fast noise thermometry and its applications
• Understanding and improving thermal boundary resistance between solids and helium
• Origins of heat leaks in low temperature apparatus.

Early work in these areas was highlighted by the Institute of Physics in their 2014 document Inspirational physics for a modern economy.

The most recent advance has been the construction of a fully-engineered high-performance cryogen-free platform for microkelvin-range refrigeration [1], based on an earlier proof-of-principle [2], which achieved sub millikelvin temperatures in a cryogen-free environment for the first time.

The solution to the problem of ultralow temperature thermometry has been the development of a current sensing noise thermometer [3-5]. This device is currently being used to establish a methodology to achieve measurements of thermodynamic temperature, to be encoded in the Mise en Pratique of the new definition of the Kelvin. Redefinition of the SI base units, links Kelvin directly to the Boltzmann constant. 

The trick has been to improve the “speed” of these thermometers by at least 4 orders of magnitude. Noise thermometers are no longer “slow”. This is graphically illustrated by our recent use of them to measure heat capacity from 200 µK to 80 mK [6].

A further goal to produce a new generation of cryogenic heat exchanger materials through developing a fundamental understanding of the thermal boundary resistance, which is currently lacking. The target is more efficient cryostats and enhanced cooling of mesoscopic samples.  Here our breakthrough is to combine a current sensing noise thermometer, with tiny heat leaks of order fW, to a metal foil sample, of typical area 1 cm2. This is enabling us to unambiguously measure the thermal boundary resistance between candidate materials and helium, uncomplicated by other factors playing an important role in large area sintered metallic particle heat exchangers.

Finally we are performing careful measurements of residual heat leaks to metallic samples.

This is motivated by the need to understand heating by cosmic-rays, radiogenic background in the cryostat, important for dark matter searches and understanding phase transitions in the early universe as part of QUEST-DMC. Moreover these measurements are of fundamental significance as they set limits on gravitationally induced wavefunction collapse (Diosi-Penrose model), a suggested probe of the quantum nature of gravity. This latter work is in collaboration with Andrea Vinante (Trento) and Hendrik Ulbricht (Southampton).