Expanding the Toolbox for Quantum Control of Atomic Qudits

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This project uses the hyperfine degrees of freedom of laser cooled cesium atoms as a testbed on which to develop and test new tools for quantum control and measurement. Qubits and qudits (d-level quantum systems) encoded in atomic ground hyperfine states are especially useful for such work because they provide long coherence times, can be coherently manipulated with radiofrequency and microwave fields, and can be probed weakly or strongly with optical fields. Efforts will be focused on two closely related areas of research. The first concerns control and measurement of quantum systems with complex internal structure, and has as its primary objectives to implement unitary control of qubits and qudits encoded in the 16-dimensional hyperfine ground manifold, to explore methods to prepare arbitrary mixed states and implement completely positive maps, and to improve or develop new protocols for quantum state and process tomography based on weak measurement and augmented by new ideas such as compressed sensing. The second focus area relates to quantum control on real world platforms, and has as its primary goals to improve and extend tools for robust qudit control in inhomogeneously broadened quantum systems, and to apply these to atoms in optical dipole traps and optical nanofiber surface traps. The research is primarily experimental, but numerical simulation and more formal theoretical study will also be undertaken.The field of Quantum Information Science (QIS) is motivated by the promise of transformative approaches to computation, communication, and ultra-precise measurement. It has also inspired new ways of thinking about old problems and unresolved issues in physics, and played a role in quantum simulations that study the real-world applicability of idealized theoretical models. QIS is now pursued in many contexts, including nanofabricated condensed matter systems, cold atoms and ions, linear and nonlinear optical systems, and various hybrids thereof. Though details vary with the physics at hand, one of the most fundamental challenges of QIS is universal: one must prepare the relevant quantum system in a well defined initial state, drive it though a complex evolution, and access the final state through measurement. In doing so, many of the tools developed on one platform can be applied to another. This project will use cold atoms as a testbed for control of quantum systems that have more than two levels. The resulting toolbox is likely to be useful and perhaps essential in the many implementations where carriers of quantum information have complex internal structure. The project will also contribute to the training of future scientists in the highly interdisciplinary field of QIS. Students will be involved in all aspects of the project, including education, research, and the dissemination of results. The project is a cornerstone of the NSF supported Center for Quantum Information and Control, co-located at the University of Arizona College of Optical Science and the University of New Mexico Department of Physics and Astronomy. Weekly video conferencing, an annual research retreat, and joint participation in conferences will enrich the educational experience and strengthen the connections between junior and senior participants at both institutions.