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Abstract

It is shown that for qubits and qutrits it is always possible to perfectly recover quantum coherence by using only classical side-information extracted from the environment, whereas for dimension d>3 there are situations where recovery is impossible, even with complete access to the environment. The Quantum Eraser [Scully, Englert, and Walther, Nature 351, 111 (1991)] in a double-slit interference experiment is reviewed as a particularly striking example of more general coherence-restoring procedures. For qubits, the minimal amount of classical side-information to be extracted from the environment is calculated to be equal to the entropy exchange.