The research supported by this grant will investigate the nature of the boundary between classical and quantum physics by study of systems consisting of a macroscopic oscillator strongly coupled to a microscopic electrical device. The microscopic device will be driven by application of an electrical signal, and its effects (or backaction) on the macroscopic oscillator will then be observed. Two systems are envisioned: in one the microscopic part is a quantum point contact (a microscopic electrical constriction in a semiconductor) and the oscillator is the macroscopic crystal in which the point contact is embedded. In the other, the microscopic part is a single Cooper pair transistor (a superconducting device that transfers Cooper pairs one by one) coupled to a superconducting microwave resonator. In each case, applying an electrical drive to the microscopic device is expected to lead to oscillations in the macroscopic oscillator. A detailed study of this interaction could lead to a better understanding of the interface between quantum and classical behavior. Two graduate students will be supported by this project, and will be trained in such experimental techniques as microwave measurement, nanoscale fabrication and low-temperature physics that are widely used both in academia and in high-technology industry.
It is well understood that the physical behavior of macroscopic objects like baseballs or planets is described very accurately by the laws of classical physics developed by Newton and familiar to many from a course in freshman physics. It is equally well understood that the behavior of microscopic objects like atoms and molecules is described by the much more mysterious and counterintuitive laws of quantum physics. What is not clear is exactly where the boundary between classical behavior and quantum behavior lies. In order to investigate this question, this research will examine the behavior of systems made up of two pieces, one that by itself would behave classically, and another that on its own would behave quantum mechanically. By design, the two pieces will interact strongly with each other, so that the behavior of the combined system will be different from that of either piece in isolation. Investigations of this sort will better delineate the border between classical and quantum physics, and help us understand the influence of quantum phenomena on the everyday world around us. Two graduate students will be supported by this project, and will be trained in such experimental techniques as microwave measurement, nanoscale fabrication and low-temperature physics that are widely used both in academia and in high-technology industry.