A Local Large Deviation Principle for Inhomogeneous Birth–Death Processes

The paper considers a continuous-time birth–death process where the jump rate has an asymptotically polynomial dependence on the process position. We obtain a rough exponential asymptotic for the probability of trajectories of a re-scaled process contained within a neighborhood of a given continuous nonnegative function.     

Data Compression Limit for an Information Source of Interacting Qubits

A system of interacting qubits can be viewed as a non-i.i.d quantum information source. A possible model of such a source is provided by a quantum spin system, in which spin-1/2 particles located at sites of a lattice interact with each other. We establish the limit for the compression of information from such a source and show that asymptotically it is given by the von Neumann entropy rate. Our result can be viewed as a quantum ana-logue of Shannon's noiseless coding theorem for a class of non-i.i.d. quantum informa-tion sources. From the probabilistic point of view it is an analog of the Shannon-McMillan-Breiman theorem considered as a cornerstone of modern Information Theory. PACS: 03.67-a; 03.67.Lx     

Fast Jackson Networks with Dynamic Routing

A new class of models of queueing networks with load-balanced dynamic routing is considered. We propose a sufficient condition for positive recurrence of the arising Markov process and a limiting mean-field approximation where the process becomes deterministic and is described by a system of nonlinear ordinary differential equations.     

On a Sufficient Condition for Additivity in Quantum Information Theory

In this paper we give a sufficient condition for additivity of the minimum output entropy for a pair of given channels and an analytic verification of this condition for specific quantum channels breaking a closely related multiplicativity property [1, 2]. This yields validity of the additivity conjecture for these channels, a result obtained by a different method in [3]. Our proof relies heavily upon certain concavity properties of the output entropy, which are of independent interest.__________Translated from Problemy Peredachi Informatsii, No. 2, 2005, pp. 9–25.Original Russian Text Copyright © 2005 by Datta, Holevo, Suhov.This work was initiated when the second author was an overseas visiting scholar at St John’s College, Cambridge. Afterwards he was supported by the Russian Scientific School Program, project no. 1758.2003.1. The first and third authors worked in association with the CMI, University of Cambridge - MIT.     

A Spectral Method for the Time Evolution in Parabolic Problems

Numerical time propagation of linear parabolic problems is commonly performed by Taylor expansion based schemes, such as Runge–Kutta. However, explicit schemes of this type impose a stringent stability restriction on the time step when the space discretization matrix is poorly conditioned. Thus the computational work required for integration over a long and fixed time interval is controlled by stability rather than by accuracy of the scheme. We develop an improved time evolution scheme based on a new Chebyshev series expansion for solving time-dependent inhomogeneous parabolic initial-boundary value problems in which the stability condition is relaxed. Spectral accuracy of the time evolution scheme is achieved. Additionally, the approximation derived here can be useful for solving quasi-linear parabolic evolution problems by exponential time differencing methods     

Multi-access system with many users: Stability and metastability

A model of random multi-access system with an ALOHA-type protocol is analyzed when the number N of users is large and the system is overloaded. In the limit as N → ∞, the behavior of the system is described by a nonrandom dynamical system. We give a condition for the dynamical system to have an attractive fixed point and outline cases of several fixed points. The presence of several fixed points indicates that the finite system may exhibit a metastability phenomenon.     

Entanglement assisted classical capacity of a class of quantum channels with long-term memory

In this paper we evaluate the entanglement assisted classical capacity of a class of quantum channels with long-term memory, which are convex combinations of memoryless channels. The memory of such channels can be considered to be given by a Markov chain which is aperiodic but not irreducible. This class of channels was introduced by Datta and Dorlas in (J. Phys. A, Math. Theor. 40:8147–8164, 2007), where its product state capacity was evaluated.      

An Accurate Polynomial Approximation of Exponential Integrators

Numerical time propagation of semi-linear equations such as reaction–diffusion, non-linear Schrödinger or semi-linear wave equations can be performed by the use of exponential time differencing. However, the evaluation of exponential integrators poses a serious technical complexity, particularly in multiple dimensions. In this paper we approach this difficulty by deriving simple polynomial series approximations of exponential integrators. Several numerical examples are presented.