Quantum Phase Transitions in Unconventional Josephson Arrays

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****NON-TECHNICAL ABSTRACT****This award supports experimental research in the ultra-low-temperature physics of quantum solid-state systems. The research focuses on the design, fabrication and characterization of a novel class of large arrays of sub-micron Josephson junctions (tunnel junctions between superconductors). Implementation of the proposed research will contribute to better understanding of several fundamental open problems in the physics of disordered systems, including the quantum phase transitions and glassy effects in a broad range of application-relevant solid-state systems. Exploration of these issues is conceptually important for better understanding of the origin of the decoherence of quantum systems, and relevant to the implementation of quantum computing with solid-state elements. The undergraduate and graduate students involved in this research receive rigorous training in advanced experimental techniques, and are prepared for careers in either an academic or industrial environment. ****TECHNICAL ABSTRACT****The proposed research focuses on the fundamental unsolved problems of the physics of quantum disordered systems, including quantum phase transitions in systems with and without long-range interactions, emergent glassy behavior, and formation of topological phases. These physical problems will be addressed by the study of charge transport in novel types of the arrays of sub-micron Josephson junctions with unconventional geometry: arrays with a large number of nearest-neighbor elements, arrays with a large number of junctions per unit cell, and arrays with non-trivial topologies. The experiments will provide an important test of different models of the "bosonic" superconductor-insulator transition, shed light on the long-standing issue of the enigmatic "metallic" phase frequently observed in Josephson arrays and ultra-thin superconducting films, and address fundamental open questions of the physics of electronic glasses. Exploration of these issues is conceptually important for better understanding of the origin of the decoherence and noise in quantum systems at low temperatures. Implementation of this research fosters training of both undergraduate and graduate students who will be exposed to the state-of-the-art tools of modern solid-state research, and can pursue careers in either an academic or industrial environment.