Mechanical Quantum Resonators: Quantum Optics with Phonons

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****NON-TECHNICAL ABSTRACT****:Quantum mechanics controls the behavior of very small, atomic-scale systems like the hydrogen atom and the electron. Demonstrations of the applicability of quantum mechanics to larger scale systems, especially ones with millions or more independent atoms, are challenging due to the need to isolate the system of interest from the environment that surrounds them, an environment that demolishes the quantum effects so peculiar to our classical experience. To date, no clear demonstration of quantum effects in large systems has been performed, certainly not in large mechanical systems. This project will focus on the construction of small mechanical resonators, similar to quartz crystals used to time computer circuits, sufficiently disconnected from the rest of the world to allow quantum effects to be displayed in an unambiguous fashion. In particular, the quantum nature of vibrational energy, which is predicted to change in steps rather than in a continuous fashion, will be explored in detail. The multidisciplinary project integrates research and education in order to train students and postdoctoral researchers in modern methods required to address this key problem in physics, which will be integrated with engineering and nanotechnology to achieve the goals set forward here. The acquired interdisciplinary skills, which include state-of-the-art nanofabrication and radiofrequency and microwave technology, prepare the trainees for careers in academe, national laboratories, and industry.****TECHNICAL ABSTRACT****:This project will investigate mechanical resonators in the low-temperature, single-phonon quantum regime. The study will focus on a novel type of high quality factor, GHz frequency piezoelectric resonator, which can have an unprecedented quality factor in this frequency band. The quantum mechanical properties of the resonators, especially in the single-phonon regime, will be probed by Josephson junction circuits recently developed for applications to superconducting quantum computation. A resonator coupled to one or more Josephson junctions provides a beautiful solid-state analog to cavity quantum electrodynamics, and this project will explore a variety of quantum optical phenomena with the coherent phonons. The goals of the project are to reveal values for the relaxation time and the coherence time of the resonator, allowing a first connection to the classical quality factor; to demonstrate "quantum refrigeration", removing individual phonons from a resonator with multi-phonon occupation; and to pursue squeezing effects controlled by the Josephson junction qubit. This would comprise the first demonstration of quantum mechanics in a macroscopic mechanical system, and a milestone in quantum physics. The multidisciplinary project integrates research and education in order to train students and postdoctoral researchers in modern methods required to address this key problem in physics, which will be integrated with engineering and nanotechnology to achieve the goals set forward here.