Quantum from Classical: Approaching the Single-Quantum Strong Coupling Regime

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Non-Technical AbstractIt is well understood that the physical behavior of macroscopic objects, like baseballs or planets, is described very accurately by the laws of classical mechanics 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 mysterious and counter-intuitive 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 mechanical systems that would normally behave classically, with the goal of causing them to instead behave quantum mechanically. This will be accomplished by using a superconducting device to cause very strong coupling between light and a mechanical resonator; the light will be used to both induce and read out the quantum behavior. 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. The PI will also collaborate with a local high school physics teacher to help enrich the local curriculum and expose high school students to cutting-edge science.Technical AbstractThe research supported by this grant will investigate the nature of the boundary between classical and quantum physics by study of systems consisting of a small mechanical resonator strongly coupled to a superconducting microwave cavity. Coupling between the two will be mediated by a single Cooper pair transistor (a superconducting device that transfers Cooper pairs one by one). The presence of the Cooper pair transistor will allow a very strong, nonlinear coupling between photons in the cavity and quantum lattice vibrations (phonons) in the mechanical resonator. This coupling will be so strong, when properly enhanced, that it should be possible to measure or influence a single phonon with a single photon. By making use of this strong, nonlinear coupling, it should be possible to use photons in the microwave cavity to induce highly quantum mechanical states of motion in the mechanical resonator. 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 industryThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.