830 research outputs found
Stability of Solution of the Nonlinear Schr\"odinger Equation for the Bose-Einstein Condensation
We investigate the stability of the Bose-Einstein condensate (BEC) the case
of atoms with negative scattering lengths at zero temperature using the
Ginzburg-Pitaevskii-Gross (GPG) stationary theory. We have found a new exact
equation for determining the upper bound of the critical numbers of
atoms for a metastable state to exist. Our calculated value of for
Bose-Einstein condensation of lithium atoms based on our new equation is in
agreement with those observed in a agreement with those observed in a recent
experiment.Comment: 8 pages, Late
Leptoquark Pair Production in \gamma\gamma Scattering: Threshold Resummation
The possibilities to pair-produce leptoquarks in photon-photon collisions are
discussed. QCD threshold corrections lead to a strong enhancement of the
production cross section. Suitably long-lived leptoquarks (\Gamma_\Phi \lsim
100 \MeV) may form Leptoquarkonium states.Comment: 7 pages LATEX, 2 eps figures. Contribution to the Proceedings of the
\gamma \gamma Workshop, 200
Tailoring and enhancing spontaneous two-photon emission processes using resonant plasmonic nanostructures
The rate of spontaneous emission is known to depend on the environment of a
light source, and the enhancement of one-photon emission in a resonant cavity
is known as the Purcell effect. Here we develop a theory of spontaneous
two-photon emission for a general electromagnetic environment including
inhomogeneous dispersive and absorptive media. This theory is used to evaluate
the two-photon Purcell enhancement in the vicinity of metallic nanoparticles
and it is demonstrated that the surface plasmon resonances supported by these
particles can enhance the emission rate by more than two orders of magnitude.
The control over two-photon Purcell enhancement given by tailored
nanostructured environments could provide an emitter with any desired spectral
response and may serve as an ultimate route for designing light sources with
novel properties
Scattering Suppression from Arbitrary Objects in Spatially-Dispersive Layered Metamaterials
Concealing objects by making them invisible to an external electromagnetic
probe is coined by the term cloaking. Cloaking devices, having numerous
potential applications, are still face challenges in realization, especially in
the visible spectral range. In particular, inherent losses and extreme
parameters of metamaterials required for the cloak implementation are the
limiting factors. Here, we numerically demonstrate nearly perfect suppression
of scattering from arbitrary shaped objects in spatially dispersive
metamaterial acting as an alignment-free concealing cover. We consider a
realization of a metamaterial as a metal-dielectric multilayer and demonstrate
suppression of scattering from an arbitrary object in forward and backward
directions with perfectly preserved wavefronts and less than 10% absolute
intensity change, despite spatial dispersion effects present in the composite
metamaterial. Beyond the usual scattering suppression applications, the
proposed configuration may serve as a simple realisation of scattering-free
detectors and sensors
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