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 $\psi(x_{\rm a},x_{\rm b})\propto (\alpha x_{\rm a}+\beta x_{\rm b})e^{-(x_{\rm a}^2+x_{\rm b}^2)/2}$. 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

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 $\lambda-$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

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