CAREER: Probing Quantum Behavior in Qubit-Coupled Nanomechanical Systems

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**Non-Technical Abstract**Quantum mechanics was developed to account for phenomena at unimaginably small scales - the realm of atoms and fundamental particles. Yet, remarkably, it has been tested without failure in an experimental domain that now extends from the constituents of matter to a wide range of engineered devices. This begs an important fundamental question: What is the nature of the boundary between the quantum and classical worlds? This Faculty Early Career Development (CAREER) project will pursue experimental studies at the boundary of the quantum and classical worlds using state-of-the-art nano-scale structures. Experiments will be performed using cryogenic measurement techniques to elicit and observe fragile quantum properties of the nanoscale structures which are typically masked by classical effects. Successful implementation of the measurements will enable tests of theories about how quantum systems "transition" to the classical regime. Moreover, the project will support the training of a postdoc and a graduate student in cutting-edge nanofabrication, cryogenics and sensitive measurement techniques. It will educate both in a broad range of contemporary physics research topics including superconducting devices and quantum measurement, and will foster international student exchange through the proposed collaboration. The research will also be incorporated into an undergraduate quantum mechanics course and tutorials geared to enhance students' understanding of the quantum world and its role in modern technology.**Technical Abstract**The experiments in this Faculty Early Career Development (CAREER) project aim to study the dynamics of coupled nanomechanical structures in the quantum regime. The project will involve the integration of a superconducting qubit to mediate a beam-splitter-type interaction between flexural modes of the nanomechanical elements. This interaction will be explored in a series of measurements using a low-loss superconducting microwave resonator to dispersively probe the quantum state of the joint system. Spectroscopy of the qubit will be performed to observe the hybridization of the coupled devices; and time-domain manipulations of the qubit will be used to generate entanglement between the qubit and the eigenmodes of the coupled nanomechanical resonators. Successful implementation of the project will enable studies of decoherence in nanomechanical systems and will be of general relevance to the quantum computing and measurement communities. The project will support the training of a postdoc and a graduate student in nanofabrication, cryogenic and microwave measurement techniques, and it will educate both in a broad range of contemporary physics research topics including superconducting devices and quantum measurement. The research will also be incorporated into an undergraduate quantum mechanics course and tutorials geared to enhance students' understanding of the quantum world and its role in modern technology.