2,971 research outputs found
Encoding for the Blackwell Channel with Reinforced Belief Propagation
A key idea in coding for the broadcast channel (BC) is binning, in which the
transmitter encode information by selecting a codeword from an appropriate bin
(the messages are thus the bin indexes). This selection is normally done by
solving an appropriate (possibly difficult) combinatorial problem. Recently it
has been shown that binning for the Blackwell channel --a particular BC-- can
be done by iterative schemes based on Survey Propagation (SP). This method uses
decimation for SP and suffers a complexity of O(n^2). In this paper we propose
a new variation of the Belief Propagation (BP) algorithm, named Reinforced BP
algorithm, that turns BP into a solver. Our simulations show that this new
algorithm has complexity O(n log n). Using this new algorithm together with a
non-linear coding scheme, we can efficiently achieve rates close to the border
of the capacity region of the Blackwell channel.Comment: 5 pages, 8 figures, submitted to ISIT 200
Generalized uncertainty relations: Theory, examples, and Lorentz invariance
The quantum-mechanical framework in which observables are associated with
Hermitian operators is too narrow to discuss measurements of such important
physical quantities as elapsed time or harmonic-oscillator phase. We introduce
a broader framework that allows us to derive quantum-mechanical limits on the
precision to which a parameter---e.g., elapsed time---may be determined via
arbitrary data analysis of arbitrary measurements on identically prepared
quantum systems. The limits are expressed as generalized Mandelstam-Tamm
uncertainty relations, which involve the operator that generates displacements
of the parameter---e.g., the Hamiltonian operator in the case of elapsed time.
This approach avoids entirely the problem of associating a Hermitian operator
with the parameter. We illustrate the general formalism, first, with
nonrelativistic uncertainty relations for spatial displacement and momentum,
harmonic-oscillator phase and number of quanta, and time and energy and,
second, with Lorentz-invariant uncertainty relations involving the displacement
and Lorentz-rotation parameters of the Poincar\'e group.Comment: 39 pages of text plus one figure; text formatted in LaTe
A Quantum Teleportation Game
We investigate a game where a sender (Alice) teleports coherent states to two
receivers (Bob and Charlie) through a tripartite Gaussian state. The aim of the
receivers is to optimize their teleportation fidelities by means of local
operations and classical communications. We show that a non-cooperative
strategy, corresponding to the standard telecloning protocol, can be
outperformed by a cooperative strategy, which gives rise to a novel
(cooperative) telecloning protocol.Comment: Typographic corrections 4 pages, 4 figure
Weak force detection with superposed coherent states
We investigate the utility of non classical states of simple harmonic
oscillators, particularly a superposition of coherent states, for sensitive
force detection. We find that like squeezed states a superposition of coherent
states allows displacement measurements at the Heisenberg limit. Entangling
many superpositions of coherent states offers a significant advantage over a
single mode superposition states with the same mean photon number.Comment: 6 pages, no figures: New section added on entangled resources.
Changes to discussions and conclusio
How to measure squeezing and entanglement of Gaussian states without homodyning
We propose a scheme for measuring the squeezing, purity, and entanglement of
Gaussian states of light that does not require homodyne detection. The
suggested setup only needs beam splitters and single-photon detectors. Two-mode
entanglement can be detected from coincidences between photodetectors placed on
the two beams.Comment: 4 pages, 2 figures, RevTe
Epidemic model with isolation in multilayer networks
The Susceptible-Infected-Recovered (SIR) model has successfully mimicked the propagation of such airborne diseases as influenza A (H1N1). Although the SIR model has recently been studied in a multilayer networks configuration, in almost all the research the isolation of infected individuals is disregarded. Hence we focus our study in an epidemic model in a two-layer network and we use an isolation parameter w to measure the effect of quarantining infected individuals from both layers during an isolation period tw. We call this process the Susceptible-Infected-Isolated-Recovered (SIIR) model. Using the framework of link percolation we find that isolation increases the critical epidemic threshold of the disease because the time in which infection can spread is reduced. In this scenario we find that this threshold increases with w and tw. When the isolation period is maximum there is a critical threshold for w above which the disease never becomes an epidemic. We simulate the process and find an excellent agreement with the theoretical results.We thank the NSF (grants CMMI 1125290 and CHE-1213217) and the Keck Foundation for financial support. LGAZ and LAB wish to thank to UNMdP and FONCyT (Pict 0429/2013) for financial support. (CMMI 1125290 - NSF; CHE-1213217 - NSF; Keck Foundation; UNMdP; Pict 0429/2013 - FONCyT)Published versio
Epidemic Model with Isolation in Multilayer Networks
The Susceptible-Infected-Recovered (SIR) model has successfully mimicked the
propagation of such airborne diseases as influenza A (H1N1). Although the SIR
model has recently been studied in a multilayer networks configuration, in
almost all the research the isolation of infected individuals is disregarded.
Hence we focus our study in an epidemic model in a two-layer network, and we
use an isolation parameter to measure the effect of isolating infected
individuals from both layers during an isolation period. We call this process
the Susceptible-Infected-Isolated-Recovered () model. The isolation
reduces the transmission of the disease because the time in which infection can
spread is reduced. In this scenario we find that the epidemic threshold
increases with the isolation period and the isolation parameter. When the
isolation period is maximum there is a threshold for the isolation parameter
above which the disease never becomes an epidemic. We also find that epidemic
models, like overestimate the theoretical risk of infection. Finally, our
model may provide a foundation for future research to study the temporal
evolution of the disease calibrating our model with real data.Comment: 18 pages, 5 figures.Accepted in Scientific Report
Photoemissive Determination of Barrier Shape in Tunnel Junctions
Tunnel junctions have been characterized
in terms of three parameters, the barrier
heights φ_1, and φ_2, and the width S, which generally
are determined by a fit of experimental
current-voltage characteristic curves with theory.
In metal-semiconductor systems barrier
heights have been determined independently
of other parameters from measurement of the
spectral dependence of photoresponse. We
wish to report the first results of the application
of this technique to the measurement of
the barrier heights in Al-Al_2O_3-A1 and Al-A1_20_3—Au tunnel junctions where the Al_2O_3 thickness
is in the range of 20 to 40 Å 
- …