Adiabatic Demagnetization Refrigerator for the Characterization of High-Performance Superconducting Quantum Circuits

点击翻译按钮获取中文摘要

In this grant application I request funding for an adiabatic demagnetization refrigerator (ADR), a type of cryostat that makes it possible to cool small mechanical objects and electronic devices to a temperature of a few thousandths of a degree above the absolute thermodynamic zero (= -273.15 degrees on the Celsius scale). This cryostat has the unique feature in that it does not require any cryogenic liquids, or the rare and expensive helium-3 gas, to reach such low temperatures. A special pulse tube pre-cools the cryostat to approximately -270 degrees Celsius. The system is further cooled by means of an adiabatic demagnetization cycle. This process is similar to a rubber band cooling: You start by stretching a rubber band slowly (i.e., isothermally) so that the generated heat is dissipated. You then rapidly (i.e., adiabatically) de-stretch it and you immediately measure its temperature. You will find that the rubber band is colder than at the beginning of the experiment. The use of a paramagnetic salt instead of a rubber band and of a magnetic field to "stretch/de-stretch" the salt allows temperatures to reach close to absolute zero. Temperature is proportional to energy: The higher the temperature of a system, the larger its thermal energy. A quantum-mechanical system is characterized by a discrete set of states, each with its own energy. In order to unveil the quantum-mechanical properties of a given system, its thermal energy must be significantly lower than the energy separation between the system lowest states. In this project, we will use an ADR to cool nano-fabricated superconducting circuits below the threshold temperature required to show their quantum-mechanical behavior. The ADR is a fast and efficient tool to characterize such quantum circuits, and it will allow us to choose the best superconducting materials to optimize the devices' performance. This is a critical task in the longstanding quest towards the implementation of a solid-state quantum computer. I believe the ADR will make it possible to improve the quality of superconducting quantum circuits by a factor ten within the next year. Both the physics community and Canada as a nation will benefit from gaining a technological expertise in the nano-fabrication of high-performance solid-state devices.