7,988 research outputs found
Wigner representation for polarization-momentum hyperentanglement generated in parametric down conversion, and its application to complete Bell-state measurement
We apply the Wigner function formalism to the study of two-photon
polarization-momentum hyperentanglement generated in parametric down
conversion. It is shown that the consideration of a higher number of degrees of
freedom is directly related to the extraction of additional uncorrelated sets
of zeropoint modes at the source. We present a general expression for the
description of the quantum correlations corresponding to the sixteen Bell base
states, in terms of four beams whose amplitudes are correlated through the
stochastic properties of the zeropoint field. A detailed analysis of the two
experiments on complete Bell-state measurement included in [Walborn et al.,
Phys. Rev. A 68, 042313 (2003)] is made, emphasizing the role of the zeropoint
field. Finally, we investigate the relationship between the zeropoint inputs at
the source and the analysers, and the limits on optimal Bell-state measurement.Comment: 28 pages, 4 figure
Partial Bell-state analysis with parametric down conversion in the Wigner function formalism
We apply the Wigner function formalism to partial Bell-state analysis using
polarization entanglement produced in parametric down conversion. Two-photon
statistics at a beam-splitter are reproduced by a wavelike description with
zeropoint fluctuations of the electromagnetic field. In particular, the
fermionic behaviour of two photons in the singlet state is explained from the
invariance on the correlation properties of two light beams going through a
balanced beam-splitter. Moreover, we show that a Bell-state measurement
introduces some fundamental noise at the idle channels of the analyzers. As a
consequence, the consideration of more independent sets of vacuum modes
entering the crystal appears as a need for a complete Bell-state analysis
Adsorbate surface diffusion: The role of incoherent tunneling in light particle motion
The role of incoherent tunneling in the diffusion of light atoms on surfaces
is investigated. With this purpose, a Chudley-Elliot master equation
constrained to nearest neighbors is considered within the Grabert-Weiss
approach to quantum diffusion in periodic lattices. This model is applied to
recent measurements of atomic H and D on Pt(111), rendering friction
coefficients that are in the range of those available in the literature for
other species of adsorbates. A simple extension of the model has also been
considered to evaluate the relationship between coverage and tunneling, and
therefore the feasibility of the approach. An increase of the tunneling rate
has been observed as the surface coverage decreases.Comment: 7 pages, 2 figures; important reorganization of the work (including
title changes
Phonon lineshapes in atom-surface scattering
Phonon lineshapes in atom-surface scattering are obtained from a simple
stochastic model based on the so-called Caldeira-Leggett Hamiltonian. In this
single-bath model, the excited phonon resulting from a creation or annihilation
event is coupled to a thermal bath consisting of an infinite number of harmonic
oscillators, namely the bath phonons. The diagonalization of the corresponding
Hamiltonian leads to a renormalization of the phonon frequencies in terms of
the phonon friction or damping coefficient. Moreover, when there are adsorbates
on the surface, this single-bath model can be extended to a two-bath model
accounting for the effect induced by the adsorbates on the phonon lineshapes as
well as their corresponding lineshapes.Comment: 14 pages, 2 figure
A generalized Chudley-Elliott vibration-jump model in activated atom surface diffusion
Here the authors provide a generalized Chudley-Elliott expression for
activated atom surface diffusion which takes into account the coupling between
both low-frequency vibrational motion (namely, the frustrated translational
modes) and diffusion. This expression is derived within the Gaussian
approximation framework for the intermediate scattering function at low
coverage. Moreover, inelastic contributions (arising from creation and
annihilation processes) to the full width at half maximum of the quasi-elastic
peak are also obtained.Comment: (5 pages, 2 figures; revised version
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