Showing papers on "Coherent information published in 1991"

Entropy production and nonequilibrium stationarity in quantum dynamical systems

Abstract: In statistical physics, Kubo's linear response theory is well known as the most effective method, in the linear-approximation regimes, of calculating transport coefficients which describe dissipative aspects in the macroscopic manifestations of microscopic quantum systems. From the viewpoint of the mutual relationship between the microscopic and macroscopic levels, it is clear that the response theory is essentially concerned with the information-theoretical problems. For lack of such key-concepts as entropy and/or entropy production, however, this theory has long been taken in physics merely as a calculational device, without the deep understanding of the reason for its general validity.

Information theory and energy spectra.

Abstract: We examine the possibility of inferring energy spectra and their concomitant eigenstates on the basis of incomplete information concerning the system's ground state. In addition, the possibility of considering, as prior information, the expectation values of a partially unknown Hamiltonian also is examined and shown to be feasible.

Rigorous derivation of error probability in coherent optical communication

Abstract: The optical communication theory has been developed in the fields of both mathematics and engineering, and it has become very important recently. In this paper we mathematically treat quantum control communication processes from information theoretical points of view, and we derive error probabilities for a concrete quantum channel in each digital modulation and detection. In paticular, several error probabilities for a coherent state and a squeezed state are rigorously calculated. It is shown that a proper squeezed state provides us a lower error probability, namely, better efficiency for optical communication.

Information Theoretical Aspects of Quantum Mechanical Entropy

Abstract: Properties of von Neumann’s entropy of a density matrix ρ, i.e., S(ρ) = -kTrρ ln ρ, are considered within the framework of quantum information theory. Although the von Neumann entropy shares many properties with the Boltzmann, Gibbs, Shannon, Baron-Jauch entropies, in some respects there exist considerable differences (i.e., the lack of monotonicity). Besides the von Neumann entropy one can also think of other measures (or concepts) of quantum information, some of them are discussed. The — rather tricky — problem of dynamical entropy for quantum systems is treated, too.

Towards a proof of two conjectures from quantum inference concerning quantum limits to knowledge of states

Abstract: The author gives a new entropic analogue of the recently reported information theoretic limits to knowledge of states. A natural relationship between the quantum correlation information and the quantum mechanical entropy is thereby revealed. In addition some progress is made towards a rigorous proof of both results and a complete solution to the problem of asymptotic optimal measurement. In particular the author employs elementary convex analysis to prove that the optimal operator valued measure must be a rank-one projection valued measure.

Evolution of difference information during self-organization of Fermi and Bose gases

Abstract: An information-theory description is derived for transitions between stationary states during the self-organization of open systems which obey quantum statistics. A new measure of difference information is proposed. It is used to evaluate the degree of order in blackbody radiation. The evolution of difference information in the course of self-organization is discussed. An I theorem is proved.