Investigations of Quantum Coherence in Josephson Junctions and Superconducting Circuits

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****NON-TECHNICAL ABSTRACT****Recent years have seen considerable progress in the development of superconducting circuits that display remarkable quantum mechanical properties at low temperature. These circuits can be thought of as "artificial atoms". Like atoms, they can exist in different quantum mechanical states; unlike real atoms, however, the properties of these artificial atoms can be adjusted by turning various control knobs. These systems are a fascinating test bed for the exploration of fundamental concepts in quantum mechanics; in addition, they might one day be used as bits in a quantum computer. A quantum computer promises to be vastly more powerful than a conventional classical computer. Recent work has shown that defects in the materials of the superconducting circuit cause noise that destroys the quantum state of the circuit. This individual investigator award supports research to understand the underlying materials physics that governs disruption of quantum states in superconducting circuits. Electrical measurements will be combined with materials characterization tools to correlate quantum behavior with materials properties. This work will contribute to the development of improved solid-state quantum technologies, and could open the door to more accurate probes of a broad range of quantum phenomena at the nanoscale. Undergraduates and graduate students will be involved in all aspects of this research, and they will receive invaluable training in a variety of state-of-the-art nanofabrication and measurement techniques. This project receives support from the Divisions of Materials Research and Physics.****TECHNICAL ABSTRACT****Superconducting quantum circuits based on Josephson junctions form a fascinating test bed for the exploration of fundamental quantum mechanics concepts such as entanglement, decoherence, and quantum measurement. The continued development of superconducting quantum circuits as qubits and as tools to probe quantum entanglement in condensed matter systems will require new insights into the fundamental physics that governs energy relaxation and dephasing. This individual investigator award supports a project to understand the microscopic origin of microwave loss and low-frequency noise from defect states in amorphous materials. Microwave transport measurements will be combined with infrared and tunneling spectroscopy to correlate dielectric loss with microscopic materials properties. SQUID-based noise measurements will be combined with measurements of ac spin susceptibility to probe the microscopic physics of dephasing due to surface magnetic states in superconducting thin films. These investigations will pave the way to the development of scalable, tunable qubit architectures. Additionally, these experiments will educate students in a variety of state-of-the-art nanofabrication and measurement techniques. The project receives support from the Divisions of Materials Research and Physics.