title: Entanglement concentration is irreversible.
abstract: In quantum information theory, it is widely believed that entanglement concentration for bipartite pure states is asymptotically reversible. In order to examine this, we give a precise formulation of the problem, and show a trade-off relation between performance and reversibility, which implies the irreversibility of entanglement concentration. Then, we regard entanglement concentration as entangled state compression in an entanglement storage with lower dimension. Because of the irreversibility of entanglement concentration, an initial state cannot be completely recovered after the compression process and a loss inevitably arises in the process. We numerically calculate this loss and also derive for it a highly accurate analytical approximation.
authors.affiliation: Graduate School of Information Sciences, Tohoku University, Sendai 980-8579, Japan and Graduate School of Mathematics, Nagoya University, Nagoya 464-8602, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Kumagai
authors.forename: Masahito
authors.initials: M
authors.lastname: Hayashi