High-Fidelity Quantum Information Processing via Dynamical Quantum Error Control

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。量子信息处理有可能彻底改变我们对计算复杂性的理解，并以前所未有的效率解决物理模拟、组合分析和安全通信中的问题。虽然利用这种力量的前景正在推动全球范围内紧张的理论和实验努力，但突出的挑战源于这样一个事实，即量子信息比经典信息更加脆弱，原因是退相干误差，这种误差是由感兴趣的设备与周围环境之间的不可控耦合引起的。尽管量子容错理论的基本进展确保了在操作量子比特的误差足够小的情况下，原则上可以进行任意精确的量子信息处理，但相应的体系结构仍然不实用，因为它们涉及到令人望而却步的资源要求。动态量子误差控制技术提供了一种抑制退相干的策略，它避免了辅助存储和测量开销，同时仍然适用于大类物理系统。我们研究的中心主题是推动动态误差控制作为分析、综合和优化现实设备的高保真量子门的框架。关键的进步来自于建立合适的“动态校正门”，以这种方式，与未校正的门相比，净去相干显著减少。我们的计划旨在获得动态量子误差控制方法的完整控制理论特征，并对其在与量子信息处理技术直接相关的开放系统中的性能进行基准测试。该项目的科学影响将是双重的。在短期内，它将提供一种低级别的错误控制策略，以减少每个门的物理错误，潜在的直接影响是减少量子容错体系结构的开销。除了可靠的量子计算，精确实现所需的么正动力学的工具可能有利于从量子模拟到量子计量学的各种应用。从更广泛的更长期的角度来看，在这项工作过程中产生的想法的副产品也将为量子信息物理和工程的核心问题提供更多的洞察力，包括“无反馈”控制程序的最终性能限制，以及量子动力学系统中可用信息、可实现的控制和复杂性之间的根本权衡。

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.