High-Fidelity Quantum Information Processing via Dynamical Quantum Error Control

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Quantum information processing holds the potential to revolutionize our understanding of computational complexity and solve problems in physics simulations, combinatorial analysis, and secure communications with unprecedented efficiency. While the prospect of harnessing such a power is spurring an intense theoretical and experimental effort worldwide, the outstanding challenge stems from the fact that quantum information is incredibly more fragile than its classical counterpart due to decoherence errors, which are induced by the uncontrollable coupling between the device of interest and its surrounding environment. Although fundamental advances in the theory of "quantum fault-tolerance" ensure that arbitrarily accurate quantum information processing is possible in principle if the error in manipulating quantum bits is sufficiently small, the corresponding architectures remain impractical due to the prohibitive resource requirements they involve. Dynamical quantum error control techniques provide a strategy to decoherence mitigation which avoids auxiliary memory and measurement overheads, while remaining applicable to a large class of physical systems. The central theme of our research is to push dynamical error control to its full capabilities as a framework for analysis, synthesis, and optimization of high-fidelity quantum gates for realistic devices. The key advance stems from building suitable "dynamically corrected gates," in such a way that the net decoherence is substantially reduced, compared to the one suffered by uncorrected gates. Our program aims at obtaining a full control-theoretical characterization of dynamical quantum error control methods, and at benchmarking their performance in open systems of direct relevance to quantum information processing technologies.The scientific impact of the project will be twofold. In the short term, it will provide a low-level error control strategy for reducing physical errors per gate, with the potentially immediate implication of reducing overheads in quantum fault-tolerant architectures. Beside reliable quantum computation, tools for precisely implementing desired unitary dynamics could be beneficial for applications ranging from quantum simulation to quantum metrology. From a broader longer-term perspective, spin-offs of ideas developed in the course of this work will also provide additional insight into issues at the very heart of quantum information physics and engineering including the ultimate performance limits of "feedback-free" control procedures, and fundamental trade-offs between available information, achievable control,and complexity in quantum-dynamical systems.