2,718 research outputs found
Four-photon interference: a realizable experiment to demonstrate violation of EPR postulates for perfect correlations
Bell's theorem reveals contradictions between the predictions of quantum
mechanics and the EPR postulates for a pair of particles only in situations
involving imperfect statistical correlations. However, with three or more
particles, contradictions emerge even for perfect correlations. We describe an
experiment which can be realized in the laboratory, using four-photon entangled
states generated by parametric down-conversion, to demonstrate this
contradiction at the level of perfect correlations.Comment: publishe
Conditional probabilities for a single photon at a beam splitter
Published versio
Excited States of Ladder-type Poly-p-phenylene Oligomers
Ground state properties and excited states of ladder-type paraphenylene
oligomers are calculated applying semiempirical methods for up to eleven
phenylene rings. The results are in qualitative agreement with experimental
data. A new scheme to interpret the excited states is developed which reveals
the excitonic nature of the excited states. The electron-hole pair of the
S1-state has a mean distance of approximately 4 Angstroem.Comment: 24 pages, 21 figure
Reversed propagation dynamics of Laguerre-Gaussian beams in left-handed materials
On the basis of angular spectrum representation, the reversed propagation
dynamics of Laguerre-Gaussian beam in left-handed materials (LHMs) is
presented. We show that negative phase velocity gives rise to a reversed screw
of wave-front, and ultimately leads to a reversed rotation of optical vortex.
Furthermore, negative Gouy-phase shift causes an inverse spiral of Poynting
vector. It is found that the Laguerre-Gaussian beam in LHMs will present the
same propagation characteristics as the counterpart with opposite topological
charges in regular right-handed materials (RHMs). The momentum conservation
theorem insures that the tangential component of the wave momentum at the
RHM-LHM boundary is conserved. It is shown that although the linear momentum
reverses its direction, the angular momentum remains unchanged.Comment: 7 pages, 4 figure
Radius of a Photon Beam with Orbital Angular Momentum
We analyze the transverse structure of the Gouy phase shift in light beams
carrying orbital angular momentum and show that the Gouy radius
characterizing the transverse structure grows as with the
nodal number and photon angular momentum number . The Gouy radius is
shown to be closely related to the root-mean-square radius of the beam, and the
divergence of the radius away from the focal plane is determined. Finally, we
analyze the rotation of the Poynting vector in the context of the Gouy radius.Comment: 11 page
Colloidal electrophoresis: Scaling analysis, Green-Kubo relation, and numerical results
We consider electrophoresis of a single charged colloidal particle in a
finite box with periodic boundary conditions, where added counterions and salt
ions ensure charge neutrality. A systematic rescaling of the electrokinetic
equations allows us to identify a minimum set of suitable dimensionless
parameters, which, within this theoretical framework, determine the reduced
electrophoretic mobility. It turns out that the salt-free case can, on the Mean
Field level, be described in terms of just three parameters. A fourth
parameter, which had previously been identified on the basis of straightforward
dimensional analysis, can only be important beyond Mean Field. More complicated
behavior is expected to arise when further ionic species are added. However,
for a certain parameter regime, we can demonstrate that the salt-free case can
be mapped onto a corresponding system containing additional salt. The
Green-Kubo formula for the electrophoretic mobility is derived, and its
usefulness demonstrated by simulation data. Finally, we report on
finite-element solutions of the electrokinetic equations, using the commercial
software package COMSOL.Comment: To appear in Journal of Physics: Condensed Matter - special issue on
occasion of the CODEF 2008 conferenc
Geometric phases for generalized squeezed coherent states
A simple technique is used to obtain a general formula for the Berry phase
(and the corresponding Hannay angle) for an arbitrary Hamiltonian with an
equally-spaced spectrum and appropriate ladder operators connecting the
eigenstates. The formalism is first applied to a general deformation of the
oscillator involving both squeezing and displacement. Earlier results are shown
to emerge as special cases. The analysis is then extended to multiphoton
squeezed coherent states and the corresponding anholonomies deduced.Comment: 15 page
Efficient Classical Simulation of Optical Quantum Circuits
We identify a broad class of physical processes in an optical quantum circuit
that can be efficiently simulated on a classical computer: this class includes
unitary transformations, amplification, noise, and measurements. This
simulatability result places powerful constraints on the capability to realize
exponential quantum speedups as well as on inducing an optical nonlinear
transformation via linear optics, photodetection-based measurement and
classical feedforward of measurement results, optimal cloning, and a wide range
of other processes.Comment: 4 pages, published versio
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