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Generalized Controllability of Noiseless Subspaces in Quantum Systems


Quantum mechanical systems are fragile and notoriously sensitive to interference from their surrounding environments, which has long complicated the development of quantum hardware and large-scale quantum computers. Quantum Noiseless Subspaces (QNS) are a type of passive noise protection for quantum systems in which quantum states are confined to subspaces immune to the effects of the dominant noise sources in the system. This confinement presents a number of unique and interesting control challenges since control action exerted over each system must be broad enough to perform useful manipulations of the state but restricted enough to maintain the state’s confinement to a QNS. Although the problem of control in QNS’s has been addressed for a handful of specific systems, no theoretical framework for assessing controllability and control synthesis for generalized open QNS’s has existed until now. This talk will present some of our key findings in the development of such a framework—in particular, a high-level overview of how the framework can be used to profile QNS’s “start-to-finish” in models for some of the most promising quantum technologies today. The talk will be accessible to physicists, mathematicians, and control theorists, requiring only basic knowledge of quantum mechanical systems and principles.