Coherent information

About: Coherent information is a research topic. Over the lifetime, 1225 publications have been published within this topic receiving 46672 citations.

Quantum data processing

Abstract: We prove a data processing inequality for quantum communication channels, which states that processing a received quantum state may never increase the mutual information between input and output states.

Towards a geometrical interpretation of quantum-information compression

Abstract: Let S be the von Neumann entropy of a finite ensemble E of pure quantum states. We show that S may be naturally viewed as a function of a set of geometrical volumes in Hilbert space defined by the states and that S is monotonically increasing in each of these variables. Since S is the Schumacher compression limit of E, this monotonicity property suggests a geometrical interpretation of the quantum redundancy involved in the compression process. It provides clarification of previous work in which it was shown that S may be increased while increasing the overlap of each pair of states in the ensemble. As a by-product, our mathematical techniques also provide an interpretation of the subentropy of E.

Information carriers and (reading them through) information theory in quantum chemistry

Abstract: This Perspective discusses the reduction of the electronic wave function via the second-order reduced density matrix to the electron density ρ(), which is the key ingredient in density functional theory (DFT) as a basic carrier of information. Simplifying further, the 1-normalized density function turns out to contain essentially the same information as ρ() and is even of preferred use as an information carrier when discussing the periodic properties along Mendeleev's table where essentially the valence electrons are at stake. The Kullback–Leibler information deficiency turns out to be the most interesting choice to obtain information on the differences in ρ() or σ() between two systems. To put it otherwise: when looking for the construction of a functional FAB = F[ζA(),ζB()] for extracting differences in information from an information carrier ζ() (i.e. ρ(), σ()) for two systems A and B the Kullback–Leibler information measure ΔS is a particularly adequate choice. Examples are given, varying from atoms, to molecules and molecular interactions. Quantum similarity of atoms indicates that the shape function based KL information deficiency is the most appropriate tool to retrieve periodicity in the Periodic Table. The dissimilarity of enantiomers for which different information measures are presented at global and local (i.e. molecular and atomic) level leads to an extension of Mezey's holographic density theorem and shows numerical evidence that in a chiral molecule the whole molecule is pervaded by chirality. Finally Kullback–Leibler information profiles are discussed for intra- and intermolecular proton transfer reactions and a simple SN2 reaction indicating that the theoretical information profile can be used as a companion to the energy based Hammond postulate to discuss the early or late transition state character of a reaction. All in all this Perspective's answer is positive to the question of whether an even simpler carrier of information than the electron density function ρ() can be envisaged: the shape function, integrating to 1 by construction fulfils this role. On the other hand obtaining the information (or information difference) contained in one (or two) systems from ρ() or σ() can be most efficiently done by using information theory, the Kulback–Leibler information deficiency being at the moment (one of) the most advisable functionals.

Broadcasting quantum Fisher information

Abstract: It is well known that classical information can be cloned, but nonorthogonal quantum states cannot be cloned, and noncommuting quantum states cannot be broadcast. We conceive a scenario in which the object we want to broadcast is the statistical distinguishability, as quantified by quantum Fisher information, about a signal parameter encoded in quantum states. We show that quantum Fisher information cannot be cloned, while it might be broadcast even when the input states are noncommuting. This situation interpolates between cloning of classical information and no broadcasting of quantum information, and indicates a hybrid way of information broadcasting which is of particular significance from both practical and theoretical perspectives.