This award supports theoretical research and education with an aim to advance understanding of how classical dynamics arises from quantum mechanical dynamics. The quest to demonstrate behavior described by quantum mechanics in the mechanical properties of nanoscale and larger structures is of fundamental significance for understanding how the macroscopic classical world emerges by approximation from the quantum world, as well as for advancing the state of the art in ultrasensitive measurement technology. Experimental efforts are currently underway that employ either optomechanical or solid state electromechanical schemes to realize these goals. In the former schemes, the quantum coherent nature of optical cavity modes are employed to drive a typically larger-than-micronscale mechanically compliant mirror into a nonclassical state, as well as to measure this state. In the latter schemes, a controllable quantum coherent superconducting device drives a nano-to-micronscale mechanical resonator into a nonclassical state via capacitive or inductive coupling, as well as measures this state. This research project consists of three interrelated thrusts that are particularly relevant to the superconducting device schemes, commonly called ?Quantum Electromechanical Systems.? The first thrust will investigate the significance of nonlinearities in amplifier dynamics for approaching the quantum limit of displacement detection, as well as for the related issue of using detector back-action to cool the mechanical resonator to its quantum ground state. The second thrust will address the contribution of tunneling two level system defects to the damping and decoherence rates of nano-to-micronscale mechanical resonators at dilution fridge and lower temperatures. The third thrust will analyze schemes to generate and detect entangled and superposition states of nano-to-micronscale mechanical resonators, as well as measure their decoherence rates. The schemes involve superconducting qubits embedded within microwave cavities that are employed for both qubit state control and readout. This theoretical research project is closely linked to experiments.
The activity outlined in project one will provide training for a graduate student in theoretical physics. Projects two and three are intended for two rising junior undergraduates with an introductory-level understanding of quantum mechanics. Through working on the projects during their junior and senior years, they will graduate with a relatively advanced understanding of open system quantum dynamics.
Non-Technical Summary:
This award supports theoretical research and education with an aim to advance our understanding of how the familiar world governed by classical mechanics emerges from the seemingly counterintuitive laws of quantum mechanics that describe phenomena on the scale of atoms and across even smaller length scales. In close connection with experiment, the PI will study tiny mechanical resonators that are driven to oscillate by devices that are described by the rules of quantum mechanics. The operation of this sort resonator device lies at what seems like an interface between the world governed by classical mechanics and that governed by quantum mechanics. The study of these kinds of systems advances fundamental knowledge and also addresses some very practical questions, including: What are the fundamental limits of measurement? What is the most sensitive measurement device that can be made? Questions of this kind become more pressing as our science and technology press to every smaller length scales with the vision of devices, electronic and mechanical, that are perhaps only few atoms in one or more dimensions and somehow have one aspect that appears squarely in the world of quantum mechanics and others that appear to be squarely in the world of classical mechanics.
This research will provide valuable educational experiences for a graduate student in theoretical physics, as well as for junior undergraduate students with an introductory-level understanding of quantum mechanics. Through working on the projects during their junior and senior years, the undergraduate students will graduate with a relatively advanced understanding of dynamics at the ?divide? between classical and quantum mechanics.
In this project we explored the behavior of electromechanical devices that straddled the microscopic and macroscopic domains, informing our understanding of how the everyday, macroscopic world of classical objects emerges from the bizarre, microscopic world of quantum systems. In one notable result, we found that a few thousand electrons flowing down a narrow quantum wire could induce nanometer scale vibrations in the millimeter crystal base of the wire. Such a micro-macro phenomenon is akin to having a dancing flea cause Mt. Everest to sway by a few meters! This joint theory-experiment work points the way to present and future projects concerned with inducing quantum effects in macroscopic mechanical objects through the strong driving action of microscopic degrees of freedom, such as electrons, photons etc. This and related project work was largely carried out by two graduate students, both of whom have since received their PhDs. One student, Laura Remus, used her advanced knowledge gained of theoretical nanophysics and computation to secure a one year position teaching high school physics, followed by a recent appointment as a technology advisor in a patent law firm. The other student, Paul Nation, became a JSPS postdoctoral fellow in the Digital Materials Team at RIKEN, Japan, and is now a tenure track assistant professor in physics at Korea University, Seoul, Korea.
