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A Finite de Finetti Theorem for Infinite-Dimensional Systems

Christian D'Cruz, Tobias J. Osborne, Ruediger Schack

quant-pharXiv:quant-ph/0606139

Abstract

We formulate and prove a de Finetti representation theorem for finitely exchangeable states of a quantum system consisting of k infinite-dimensional subsystems. The theorem is valid for states that can be written as the partial trace of a pure state chosen from a family of subsets Cn of the full symmetric subspace for n subsystems. We show that such states become arbitrarily close to mixtures of pure power states as n increases. We give a second equivalent characterization of the family Cn.

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