28,123 research outputs found
Nonclassical Correlation of Polarization Entangled Photons in a Biexciton-Exciton Cascade
We develop a theoretical model to study the Intensity-Intensity correlation
of polarization entangled photons emitted in a biexciton-exciton cascade. We
calculate the degree of correlation and show how polarization correlation are
affected by the presence of dephasing and energy level splitting of the
excitonic states. Our theoretical calculations are in agreement with the recent
observation of polarization dependent Intensity-Intensity correlations from a
single semiconductor quantum dot [R. M. Stevenson et. al., Nature 439, 179
(2006)] . Our model can be extended to study polarization entangled photon
emission in coupled quantum dot systems
Generating aerosols for laser velocimeter seeding
The laser velocimeter (LV) is a unique tool for fluid flow measurements. In such measurements, even though the fluid velocity is of primary interest, the LV signal originates from seed particles present in the fluid and the LV actually measures the velocity of these particles. Thus it is important that a sufficient number of seed particles be present in the fluid and they scatter sufficient light to produce LV signals. Also, the seed particles should follow the fluid with high fidelity. Aerodynamic diameter is the true measure of a particle's ability to follow the flow. The aerodynamic diameter of a particle is defined as the diameter of a unit density sphere with same settling velocity as the particle in question. It is affected by geometric diameter, density and shape of the particle. For LV seeding, particles with smaller aerodynamic diameter are desirable because they follow the flow more readily. On the other hand, in general, the particle's ability to scatter light increases with its geometric diameter and its refractive index
Inseparability inequalities for higher-order moments for bipartite systems
There are several examples of bipartite entangled states of continuous
variables for which the existing criteria for entanglement using the
inequalities involving the second order moments are insufficient. We derive new
inequalities involving higher order correlation, for testing entanglement in
non-Gaussian states. In this context we study an example of a non-Gaussian
state, which is a bipartite entangled state of the form .
Our results open up an avenue to search for new inequalities to test
entanglement in non-Gaussian states.Comment: 7 pages, Submitte
Reconstruction of SU(1,1) States
We show how group symmetries can be used to reconstruct quantum states. In
our scheme for SU(1,1) states, the input field passes through a non-degenerate
parametric amplifier and one measures the probability of finding the output
state with a certain number (usually zero) of photons in each mode. The density
matrix in the Fock basis is retrieved from the measured data by least squares
method after singular value decomposition of the design matrix. Several
illustrative examples involving the reconstruction of a pair coherent state, a
Perelomov coherent state, and a coherent superposition of pair coherent states
are considered.Comment: 8 pages, 5 figures, submitted to PR
Charge transport in a nonlinear, three--dimensional DNA model with disorder
We study the transport of charge due to polarons in a model of DNA which
takes in account its 3D structure and the coupling of the electron wave
function with the H--bond distortions and the twist motions of the base pairs.
Perturbations of the ground states lead to moving polarons which travel long
distances. The influence of parametric and structural disorder, due to the
impact of the ambient, is considered, showing that the moving polarons survive
to a certain degree of disorder. Comparison of the linear and tail analysis and
the numerical results makes possible to obtain further information on the
moving polaron properties.Comment: 9 pages, 2 figures. Proceedings of the conference on "Localization
and energy transfer in nonlinear systems", June 17-21, 2002, San Lorenzo de
El Escorial, Madrid, Spain. To be publishe
Measuring arbitrary-order coherences: Tomography of single-mode multiphoton polarization-entangled states
A scheme is discussed for measuring Nth-order coherences of two orthogonally
polarized light fields in a single spatial mode at very limited experimental
cost. To implement the scheme, the only measurements needed are the Nth-order
intensity moments after the light beam has passed through two quarter-wave
plates, one half-wave plate, and a polarizing beam splitter for specific
settings of the wave plates. It is shown that this method can be applied for
arbitrarily large N. A set of explicit values is given for the settings of the
wave plates, constituting an optimal measurement of the Nth-order coherences
for any N. For Fock states the method introduced here corresponds to a full
state tomography. Applications of the scheme to systems other than polarization
optics are discussed.Comment: 6 pages, 1 figure, 1 table, published versio
Nonlinear charge transport mechanism in periodic and disordered DNA
We study a model for polaron-like charge transport mechanism along DNA
molecules with emphasis on the impact of parametrical and structural disorder.
Our model Hamiltonian takes into account the coupling of the charge carrier to
two different kind of modes representing fluctuating twist motions of the base
pairs and H-bond distortions within the double helix structure of
DNA. Localized stationary states are constructed with the help of a
nonlinear map approach for a periodic double helix and in the presence of
intrinsic static parametrical and/or structural disorder reflecting the impact
of ambient solvent coordinates. It is demonstrated that charge transport is
mediated by moving polarons respectively breather compounds carrying not only
the charge but causing also local temporal deformations of the helix structure
through the traveling torsion and bond breather components illustrating the
interplay of structure and function in biomolecules.Comment: 23 pages, 13 figure
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