959 research outputs found
Probability density function characterization of multipartite entanglement
We propose a method to characterize and quantify multipartite entanglement
for pure states. The method hinges upon the study of the probability density
function of bipartite entanglement and is tested on an ensemble of qubits in a
variety of situations. This characterization is also compared to several
measures of multipartite entanglement.Comment: 7 pages, 2 figures; published version; title changed; further
explanations and comparison with several measures of multipartite
entanglement adde
Scaling of Entanglement Entropy in the Random Singlet Phase
We present numerical evidences for the logarithmic scaling of the
entanglement entropy in critical random spin chains. Very large scale exact
diagonalizations performed at the critical XX point up to L=2000 spins 1/2 lead
to a perfect agreement with recent real-space renormalization-group predictions
of Refael and Moore [Phys. Rev. Lett. {\bf 93}, 260602 (2004)] for the
logarithmic scaling of the entanglement entropy in the Random Singlet Phase
with an effective central charge . Moreover we
provide the first visual proof of the existence the Random Singlet Phase thanks
to the quantum entanglement concept.Comment: 4 pages, 3 figure
Characterizing and measuring multipartite Entanglement
A method is proposed to characterize and quantify multipartite entanglement
in terms of the probability density function of bipartite entanglement over all
possible balanced bipartitions of an ensemble of qubits. The method is tested
on a class of random pure states.Comment: 7 pages, 5 figures. Submitted to "International Journal of Quantum
Information
Out of equilibrium correlation functions of quantum anisotropic XY models: one-particle excitations
We calculate exactly matrix elements between states that are not eigenstates
of the quantum XY model for general anisotropy. Such quantities therefore
describe non equilibrium properties of the system; the Hamiltonian does not
contain any time dependence. These matrix elements are expressed as a sum of
Pfaffians. For single particle excitations on the ground state the Pfaffians in
the sum simplify to determinants.Comment: 11 pages, no figures; revtex. Minor changes in the text; list of
refs. modifie
Simulating Visual Attention Allocation of Pilots in an Advanced Cockpit Environment
This paper describes the results of experiments conducted with human line pilots and a cognitive pilot model during interaction with a new 40 Flight Management System (FMS). The aim of these experiments was to gather human pilot behavior data in order to calibrate the behavior of the model. Human behavior is mainly triggered by visual perception. Thus, the main aspect was to setup a profile of human pilots' visual attention allocation in a cockpit environment containing the new FMS. We first performed statistical analyses of eye tracker data and then compared our results to common results of familiar analyses in standard cockpit environments. The comparison has shown a significant influence of the new system on the visual performance of human pilots. Further on, analyses of the pilot models' visual performance have been performed. A comparison to human pilots' visual performance revealed important improvement potentials
Cold atoms in non-Abelian gauge potentials: From the Hofstadter "moth" to lattice gauge theory
We demonstrate how to create artificial external non-Abelian gauge potentials
acting on cold atoms in optical lattices. The method employs internal
states of atoms and laser assisted state sensitive tunneling. Thus, dynamics
are communicated by unitary -matrices. By experimental control of
the tunneling parameters, the system can be made truly non-Abelian. We show
that single particle dynamics in the case of intense U(2) vector potentials
lead to a generalized Hofstadter butterfly spectrum which shows a complex
``moth''-like structure. We discuss the possibility to employ non-Abelian
interferometry (Aharonov-Bohm effect) and address methods to realize matter
dynamics in specific classes of lattice gauge fields.Comment: 5 pages, 3 figure
Transition from hexagons to optical turbulence
4 pages, 3 figures.-- PACS nrs.: 42.65.Sf, 47.20.Ky, 47.54.+r, 89.75.Kd.We characterize the different dynamical regimes and bifurcations in the transition from a stationary hexagonal pattern to optical turbulence. In order to characterize the bifurcations we perform linear stability analysis of stationary hexagonal patterns and Floquet analysis of oscillating hexagons. The interplay between space and time leads to a series of bifurcations showing spatial-period multiplying and quasiperiodicity.The authors acknowledge financial support from the MCyT (Spain, Project Nos. PB97-0141-C02-02, BFM2000-1108, and BFM2001-0341-C02-02).Peer reviewe
Quantum many particle systems in ring-shaped optical lattices
In the present work we demonstrate how to realize 1d-optical closed lattice
experimentally, including a {\it tunable} boundary phase-twist. The latter may
induce ``persistent currents'', visible by studing the atoms' momentum
distribution. We show how important phenomena in 1d-physics can be studied by
physical realization of systems of trapped atoms in ring-shaped optical
lattices. A mixture of bosonic and/or fermionic atoms can be loaded into the
lattice, realizing a generic quantum system of many interacting particles.Comment: 10 pages, 5 figures. To be published in PR
- …