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Thwarting long-lived dark states to speed up dynamic polarization

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Long-lived dark states, in which an experimentally accessible qubit is not in thermal equilibrium with a surrounding spin bath, are pervasive in solid-state systems. In the first half of the talk, I will explain the ubiquity of dark states in a large class of inhomogenous central spin models using the proximity to integrable lines with exact dark eigenstates. I will develop a picture of the eigenstates away from the integrable lines in terms of many-body resonances, and argue that relaxation times are exponentially large in system size at accessible sizes.

Long-lived dark states stymie hyperpolarization protocols that aim to transfer spin polarization from the central qubit to the surrounding spin bath. In the second half of the talk, I will describe fast and efficient hyperpolarization protocols that exploit certain integrability-breaking terms to reduce the statistical weight on dark states. These protocols use approximate counter-diabatic driving and are experimentally accessible through Floquet engineering.

This talk is part of the Theory of Condensed Matter series.

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