Manipulating Majorana bound states in S-TI-S Josephson junction networks: braiding, fusion, and parity dynamics

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Non-Technical Abstract:This award combines experimental condensed matter physics and quantum information science research aimed at understanding a newly-discovered class of materials and developing schemes for incorporating them into advanced electronic devices for quantum computing. The focus is on topological materials whose properties depend on the topology, or geometry, of their electronic structure, enabling novel electronic states that can carry and control currents in unique ways. Fabricating and measuring a series of advanced hybrid devices that integrate these topological materials with superconductors will enable exploration of the capabilities and limitations of this approach that has been predicted to exhibit new physical phenomena and electronic properties. In addition to their scientific interest, these unique materials can be implemented in electronic circuits to create a new type of computer platform in which the information is stored in quantum states protected from the detrimental effects of the environment, a unique feature of topological devices that has the potential to extend dramatically the speed and capability of large-scale computers. Through the new science and applications that may arise from this project, this research program exposes a diverse cadre of postdoctoral researchers, graduate research students, and undergraduate students to scientific issues and experimental techniques relevant to the development and applications of new materials and phenomena. This training at the interface of materials science and device physics has been demonstrated to be highly effective in launching the careers of scientists and engineers in high technology fields.Technical Abstract: Exciting new phenomena have been predicted to arise in hybrid superconductor-topological insulator systems in which pair correlations induce an effective complex superconducting order parameter exhibiting chiral edge states, topologically-protected surface states, and Majorana fermions, exotic excitations that are their own antiparticles. This project focuses on schemes to nucleate these exotic excitations and manipulate them in controllable ways to verify their existence and explore their stability and dynamics. A series of specific experiments are designed to reveal their unique non-Abelian statistics and to develop functional approaches to image, manipulate, readout the parity that encodes their critical phase information, and braid them to perform logical operations, all critical steps toward understanding the underlying physics of these novel states and crafting a technology for quantum information processing, quantum metrology, and quantum simulation/computing. Key experiments fall into two categories: (1) investigation and characterization of the parity dynamics of Majorana states in S-TI-S Josephson junctions and determine the materials and device properties that affect it --- this includes experiments to observe and characterize parity fluctuations, modeling of the interplay of Josephson phase dynamics and parity transitions, and ways to improve parity lifetimes, (2) development of schemes for braiding, fusion, and parity readout of Majorana modes in the S-TI-S platform, all important capabilities required to implement scheme. The field of topological physics is very new and researchers worldwide are collectively just starting to explore the materials, measurements, and theoretical concepts that will be important in achieving an understanding of Majorana fermions and how to exploit them in electronic circuits. This project explores the key unsolved problems in this field and paths for making significant advances in understanding the nature of exotic Majorana fermions and implementing them in functional superconductor circuits. It also provides opportunities to train students in the science and technology of this field that is anticipated to grow in the coming years.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.