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Nanoscale Devices for Ultralow Temperature Thermometry

Final Report Summary - NANOTEMP (Nanoscale Devices for Ultralow Temperature Thermometry)

Studies of nanoelectronic devices at low temperatures have produced many fundamental discoveries in physics and material science and have the potential to enable new applications such as future metrological standards and sensors that are enhanced by the quantum-mechanical nature of their operation. For quantum-enhanced applications, it is often important to cool the devices far below 1 Kelvin, approaching temperatures of a few millikelvin. The goal of this project was to address outstanding challenges in nanoelectronic thermometry and to provide new tools and techniques for researchers working at temperatures of a few millikelvin and below.

One outstanding challenge in this regime is how to effectively cool electrons in nanoelectronic structures. Until recently, the record low temperature in such structures had been 4 millikelvin for over 10 years. During this project we were been able to break this barrier, reaching temperatures significantly below 2 millikelvin. This was achieved using a new cooling technique that has the potential to reach sub-millikelvin temperatures, combined with with reliable thermometry of on-chip electron temperature.

Another challenge at ultralow temperatures is understanding the behaviour of the refrigerant, which can be a metal (for demagnetization cooling) or a mixture of superfluid helium-3 and helium-4 (for dilution refrigeration). Probing superfluid helium has been possible for many years using macroscopic mechanical objects. Now it is possible to use techniques from nanotechnology to create smaller probes that will provide new information about the superfluid. During this project we succeeded in measuring the damping of a nanomechanical resonator immersed in superfluid helium-4.

The project has provided valuable opportunities for the fellow to form new collaborations in Europe and to reintegrate within the UK and EU research community. As well as academic collaborations, the project has facilitated new industrial collaborations that would otherwise not have been possible.