Ultralow temperature thermometry with nanoscale devices

点击翻译按钮获取中文摘要

The goal of cooling materials and structures ever closer to absolute zero temperature has led to significant discoveries in physics and has prompted the development of many new technologies. For example, the phenomena of superfluidity and superconductivity showed that quantum-mechanical effects dominate the behaviour of certain materials at low temperatures. The discovery of the quantum Hall effect has given a new metrological standard for defining voltage, and the discovery of Coulomb blockade may soon allow the ampere to be redefined using devices that generate electrical current one electron at a time. Cooling to very low temperatures can better allow us to observe and control certain materials and structures at a quantum-mechanical level. This continues to drive research in low temperature physics and underpins many efforts to realise new quantum technologies such as quantum computation and advanced sensors.Present refrigeration technologies allow certain materials to be cooled extremely close to absolute zero. The limit for continuous cooling is around 1 millikelvin, using dilution refrigeration. Additional cooling based on nuclear demagnetisation refrigeration allows some materials can be cooled to less than a hundredth of this temperature. The biggest challenge in using either of these methods to cool an arbitrary sample is making a good thermal connection between the sample and the refrigerator. At low temperatures thermal connections between materials become very small. This can mean, for instance, that the electrons in the metal wires contacting an on-chip device are at a different temperature to that of the chip, and neither are as cold as the refrigerator. This a particular problem in the field of nanoelectronics where the sample has a tiny active volume with a very weak thermal connection to its surroundings. At present, it is extremely challenging to cool nanoelectronic samples significantly below 10 millikelvin.This project will combine techniques from ultralow temperature physics and nanotechnology to develop new devices that can measure the temperature of electrons in nanoelectronic structures below 1 millikelvin. These thermometers will then be used to build a platform for reaching temperatures of 1 millikelvin or below in arbitrary nanoelectronic samples. Three different thermometers will be studied, before the most promising one is selected for the final stage of the project. All of the thermometers will be essential diagnostic tools throughout the project, informing the development of electrical filters, thermal shielding and refrigeration methods.The new thermometry techniques will give us a better understanding of nanoscale structures in a currently inaccessible temperature range. This is likely to be a significant benefit to many active areas of research in low temperature physics, quantum computing, nanoscience and metrology.