Mixed-state certification of quantum capacities for noisy communication channels

We extend a recent method to detect lower bounds to the quantum capacity of quantum communication channels by considering realistic scenarios with general input probe states and arbitrary detection procedures at the output. Realistic certification relies on a new bound for the coherent information of a quantum channel that can be applied with arbitrary bipartite mixed input states and generalized output measurements.Comment: 7 pages, 2 figure

Upper Bounds on the Capacities of Noncontrollable Finite-State Channels with/without Feedback

Noncontrollable finite-state channels (FSCs) are FSCs in which the channel inputs have no influence on the channel states, i.e., the channel states evolve freely. Since single-letter formulae for the channel capacities are rarely available for general noncontrollable FSCs, computable bounds are usually utilized to numerically bound the capacities. In this paper, we take the delayed channel state as part of the channel input and then define the {\em directed information rate} from the new channel input (including the source and the delayed channel state) sequence to the channel output sequence. With this technique, we derive a series of upper bounds on the capacities of noncontrollable FSCs with/without feedback. These upper bounds can be achieved by conditional Markov sources and computed by solving an average reward per stage stochastic control problem (ARSCP) with a compact state space and a compact action space. By showing that the ARSCP has a uniformly continuous reward function, we transform the original ARSCP into a finite-state and finite-action ARSCP that can be solved by a value iteration method. Under a mild assumption, the value iteration algorithm is convergent and delivers a near-optimal stationary policy and a numerical upper bound.Comment: 15 pages, Two columns, 6 figures; appears in IEEE Transaction on Information Theor

Condensate formation in a zero-range process with random site capacities

We study the effect of quenched disorder on the zero-range process (ZRP), a system of interacting particles undergoing biased hopping on a one-dimensional periodic lattice, with the disorder entering through random capacities of sites. In the usual ZRP, sites can accommodate an arbitrary number of particles, and for a class of hopping rates and high enough density, the steady state exhibits a condensate which holds a finite fraction of the total number of particles. The sites of the disordered zero-range process considered here have finite capacities chosen randomly from the Pareto distribution. From the exact steady state measure of the model, we identify the conditions for condensate formation, in terms of parameters that involve both interactions (through the hop rates) and randomness (through the distribution of the site capacities). Our predictions are supported by results obtained from a direct numerical sampling of the steady state and from Monte Carlo simulations. Our study reveals that for a given realization of disorder, the condensate can relocate on the subset of sites with largest capacities. We also study sample-to-sample variation of the critical density required to observe condensation, and show that the corresponding distribution obeys scaling, and has a Gaussian or a Levy-stable form depending on the values of the relevant parameters.Comment: Contribution to the JStatMech Special Issue dedicated to the Galileo Galilei Institute, Florence Workshop "Advances in nonequilibrium statistical mechanics",v2: close to the published versio

Building Advocacy Capacity: Where Grantees Started

Describes the baseline levels of core advocacy capacities of groups participating in Consumer Voices for Coverage, a twelve-state initiative to build consumer organizations' network and advocacy capacity. Discusses lessons learned and recommendations

Q investment models, factor complementary and monopolistic competition

The observed fact that firms invest even if capacities are not fully employed does not fit well into most standard formalizations of optimal firm behavior. In this paper, the q investment approach is adapted to an imperfectly competitive economy where the representative firm is assumed to face demand uncertainty. Nominal rigidities and short-run factor complementarity are imposed as sufficient conditions to allow for the coexistence of investment and excess capacity. Since capacities are underemployed, marginal q is shown to diverge from average q. Finally, excess capacity subsists at steady state which makes it more than a shortrun phenomeno

Difficulties of Estimating the Cost of Achieving Education Standards

Outlines the limitations of four approaches to estimating the resources needed to improve educational outcomes, including higher state standards, varied student needs, different capacities and prices for education inputs across districts, and poor data

Magic Melters' Have Geometrical Origin

Recent experimental reports bring out extreme size sensitivity in the heat capacities of Gallium and Aluminum clusters. In the present work we report results of our extensive {\it ab initio} molecular dynamical simulations on Ga$_{30}$ and Ga$_{31}$, the pair which has shown rather dramatic size sensitivity. We trace the origin of this size sensitive heat capacities to the relative order in their respective ground state geometries. Such an effect of nature of the ground state on the characteristics of heat capacities is also seen in case of small Gallium and Sodium clusters indicating that the observed size sensitivity is a generic feature of small clusters.Comment: 4 pages, 6 figure

Ready or Not? Protecting the Public's Health From Diseases, Disasters, and Bioterrorism, 2011

Highlights examples of preparedness programs and capacities at risk of federal budget cuts or elimination, examines state and local public health budget cuts, reviews ten years of progress and shortfalls, and outlines policy issues and recommendations