title: Gaussian quantum discord.
abstract: We extend the quantum discord to continuous variable systems and evaluate Gaussian quantum discord C(ϱ) for bipartite Gaussian states. In particular, for squeezed-thermal states, we explicitly maximize the extractable information over Gaussian measurements: C(ϱ) is minimized by a generalized measurement rather than a projective one. Almost all squeezed-thermal states have nonzero Gaussian discord: They may be either separable or entangled if the discord is below the threshold C(ϱ) = 1, whereas they are all entangled above the threshold. We elucidate the general role of state parameters in determining the discord and discuss its evolution in noisy channels.
authors.affiliation: ISI Foundation, I-10133 Torino, Italy. giorda@isi.it
authors.forename: Paolo
authors.initials: P
authors.lastname: Giorda
authors.forename: Matteo G A
authors.initials: MG
authors.lastname: Paris