523 research outputs found
Photon statistics without counting photons
We show how to obtain the photon distribution of a single-mode field using
only avalanche photodetectors. The method is based on measuring the field at
different quantum efficiencies and then inferring the photon distribution by
maximum-likelihood estimation. The convergence of the method and its robustness
against fluctuations are illustrated by means of numerically simulated
experiments.Comment: references added, new figure
Degradation of continuous variable entanglement in a phase-sensitive environment
We address the propagation of twin-beam of radiation through Gaussian
phase-sensitive channels, i.e. noisy channels with squeezed fluctuations. We
find that squeezing the environment always reduces the survival time of
entanglement in comparison to the case of simple dissipation and thermal noise.
We also show that the survival time is further reduced if the squeezing phase
of the fluctuations is different from the twin-beam phase.Comment: to be published in the special issue of J. Mod. Opt. (April 2004)
edited by R. Bonifacio, B.G. Englert and M.G.A. Paris, devoted to the 2003
Garda Lake Workshop on "Mysteries, Puzzles and Paradoxes in Quantum
Mechanics
Dynamical paths and universality in continuous variables open systems
We address the dynamics of quantum correlations in continuous variable open
systems and analyze the evolution of bipartite Gaussian states in independent
noisy channels. In particular, upon introducing the notion of dynamical path
through a suitable parametrization for symmetric states, we focus attention on
phenomena that are common to Markovian and non-Markovian Gaussian maps under
the assumptions of weak coupling and secular approximation. We found that the
dynamical paths in the parameter space are universal, that is they do depend
only on the initial state and on the effective temperature of the environment,
with non Markovianity that manifests itself in the velocity of running over a
given path. This phenomenon allows one to map non-Markovian processes onto
Markovian ones and it may reduce the number of parameters needed to study a
dynamical process, e.g. it may be exploited to build constants of motions valid
for both Markovian and non-Markovian maps. Universality is also observed in the
value of Gaussian discord at the separability threshold, which itself is a
function of the sole initial conditions in the limit of high temperature. We
also prove the existence of excluded regions in the parameter space, i.e. of
sets of states which cannot be linked by any Gaussian dynamical map.Comment: 7 pages, 2 figures, improved pictures and forma
Probing the sign of on-site Hubbard interaction by two-particle quantum walks
We consider two identical bosons propagating on a one-dimensional lattice and
address the prob- lem of discriminating whether their mutual on-site
interaction is attractive or repulsive. We suggest a probing scheme based on
the properties of the corresponding two-particle quantum walks, and show that
the sign of the interaction introduces specific and detectable features in the
dynamics of quantum correlations, thus permitting to discriminate between the
two cases. We also discuss how these features are connected to the
band-structure of the Hubbard Hamiltonian, and prove that discrimination may be
obtained only when the two walkers are initially prepared in a superposition of
localized states.Comment: 9 pages, 9 figure
Quantum probes to assess correlations in a composite system
We suggest and demonstrate experimentally a strategy to obtain relevant
information about a composite system by only performing measurements on a small
and easily accessible part of it, which we call quantum probe. We show in
particular how quantitative information about the angular correlations of
couples of entangled photons generated by spontaneous parametric down
conversion is accessed through the study of the trace distance between two
polarization states evolved from different initial conditions. After estimating
the optimal polarization states to be used as quantum probe, we provide a
detailed analysis of the connection between the increase of the trace distance
above its initial value and the amount of angular correlations.Comment: 6 pages, 4 figure
Eigenvalue Dynamics of a Central Wishart Matrix with Application to MIMO Systems
We investigate the dynamic behavior of the stationary random process defined
by a central complex Wishart (CW) matrix as it varies along a
certain dimension . We characterize the second-order joint cdf of the
largest eigenvalue, and the second-order joint cdf of the smallest eigenvalue
of this matrix. We show that both cdfs can be expressed in exact closed-form in
terms of a finite number of well-known special functions in the context of
communication theory. As a direct application, we investigate the dynamic
behavior of the parallel channels associated with multiple-input
multiple-output (MIMO) systems in the presence of Rayleigh fading. Studying the
complex random matrix that defines the MIMO channel, we characterize the
second-order joint cdf of the signal-to-noise ratio (SNR) for the best and
worst channels. We use these results to study the rate of change of MIMO
parallel channels, using different performance metrics. For a given value of
the MIMO channel correlation coefficient, we observe how the SNR associated
with the best parallel channel changes slower than the SNR of the worst
channel. This different dynamic behavior is much more appreciable when the
number of transmit () and receive () antennas is similar. However, as
is increased while keeping fixed, we see how the best and worst
channels tend to have a similar rate of change.Comment: 15 pages, 9 figures and 1 table. This work has been accepted for
publication at IEEE Trans. Inf. Theory. Copyright (c) 2014 IEEE. Personal use
of this material is permitted. However, permission to use this material for
any other purposes must be obtained from the IEEE by sending a request to
[email protected]
The fluctuating two-ray fading model: exact and approximate statistical characterization
El congreso en el que se ha presentado este artÃculo no genera libro de actas, por lo que el copyright no se ha transferido a IEEE.We introduce the Fluctuating Two-Ray (FTR) fading model, a new statistical channel model that consists of two fluctuating specular components with random phases plus a diffuse component. The PDF and MGF are expressed in closed-form, having a functional form similar to other state-of-the-art fading models. We also provide an approximate closed-form expressions for the PDF, which allow for a simple evaluation of these statistics to an arbitrary level of precision. We show that the FTR fading model provides a much better fit than Rician fading for recent small-scale fading measurements in 28 GHz outdoor millimeter-wave channels.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech. Proyecto MINECO-FEDER TEC2013-42711-R, TEC2014-57901-R y TEC2013-44442-P. Junta de AndalucÃa P2011-TIC-7109 y P2011-TIC-8238
The Fluctuating Two-Ray Fading Model: Statistical Characterization and Performance Analysis
(c) 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.We introduce the fluctuating two-ray (FTR) fading model, a new statistical channel model that consists of two fluctuating specular components with random phases plus a diffuse component. The FTR model arises as the natural generalization of the two-wave with diffuse power (TWDP) fading model; this generalization allows its two specular components to exhibit a random amplitude fluctuation. Unlike the TWDP model, all the chief probability functions of the FTR fading model (PDF, CDF, and MGF) are expressed in closed-form, having a functional form similar to other state-of-the-art fading models. We also provide approximate closed-form expressions for the PDF and CDF in terms of a finite number of elementary functions, which allow for a simple evaluation of these statistics to an arbitrary level of precision. We show that the FTR fading model provides a much better fit than Rician fading for recent small-scale fading measurements in 28 GHz outdoor mm-wave channels. Finally, the performance of wireless communication systems over FTR fading is evaluated in terms of the bit error rate and the outage capacity, and the interplay between the FTR fading model parameters and the system performance is discussed. Monte Carlo simulations have been carried out in order to validate the obtained theoretical expressions.Universidad de Málaga. Campus de Excelencia Internacional. AndalucÃa Tech
The Fluctuating Two-Ray Fading Model for mmWave Communications
We introduce the Fluctuating Two-Ray (FTR) fading model, a new statistical channel model that consists of two fluctuating specular components with random phases plus a diffuse component. The FTR model arises as a natural generalization of the two-wave with diffuse power (TWDP) fading model proposed by Durgin, Rappaport and de Wolf; in this extended model, the two specular components exhibit a random amplitude fluctuation. Unlike in the TWDP model, we show that all the chief probability functions of the FTR fading model (PDF, CDF and MGF) can be expressed in closed-form. We also show that the FTR fading model provides a much better fit than the Rician fading model for recent small-scale fading measurements of the 28 GHz outdoor millimeter-wave channels.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
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