11,190 research outputs found
Polarization of the electron and positron produced in combined Coulomb and strong laser fields
The process of production in the superposition of a Coulomb and a
strong laser field is considered. The pair production rate integrated over the
momentum and summed over the spin projections of one of the particles is
derived exactly in the parameters of the laser field and in the Born
approximation with respect to the Coulomb field. The case of a monochromatic
circularly polarized laser field is considered in detail. A very compact
analytical expression of the pair production rate and its dependence on the
polarization of one of the created particles is obtained in the quasiclassical
approximation for the experimentally relevant case of an undercritical laser
field. As a result, the polarization of the created electron (positron) is
derived.Comment: 16 pages, no figure
Hyperbolic carbon nanoforest for phase matching of ordinary and backward electromagnetic waves: second harmonic generation
We show that deliberately engineered dispersive metamaterial slab can enable
the co-existence and phase matching of contra-propagating ordinary fundamental
and extraordinary backward second harmonic surface electromagnetic modes.
Energy flux and phase velocity are contra-directed in the backward waves which
is the phenomenon that gives rise to unique nonlinear optical propagation
processes. We show that frequencies, phase, and group velocities, as well as
nanowaveguide losses inherent to the electromagnetic modes supported by such
metamaterial, can be tailored to maximize conversion of frequencies and to
reverse propagation direction of the generated wave. Such a possibility, which
is of paramount importance for nonlinear photonics, is proved with a numerical
model of the hyperbolic metamaterial made of carbon nanotubes standing on the
metal surface. Extraordinary properties of the backward-wave second harmonic
generation in the reflection direction and of the corresponding frequency
doubling metareflector in the THz are investigated with a focus on the pulsed
regime.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1602.0249
Unidirectional Amplification and Shaping of Optical Pulses by Three-Wave Mixing with Negative Phonons
A possibility to greatly enhance frequency-conversion efficiency of
stimulated Raman scattering is shown by making use of extraordinary properties
of three-wave mixing of ordinary and backward waves. Such processes are
commonly attributed to negative-index plasmonic metamaterials. This work
demonstrates the possibility to replace such metamaterials that are very
challenging to engineer by readily available crystals which support elastic
waves with contra-directed phase and group velocities. The main goal of this
work is to investigate specific properties of indicated nonlinear optical
process in short pulse regime and to show that it enables elimination of
fundamental detrimental effect of fast damping of optical phonons on the
process concerned. Among the applications is the possibility of creation of a
family of unique photonic devices such as unidirectional Raman amplifiers and
femtosecond pulse shapers with greatly improved operational properties.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1304.681
Information processing using three-qubit and qubit-qutrit encodings of noncomposite quantum systems
We study quantum information properties of a seven-level system realized by a
particle in an one-dimensional square-well trap. Features of encodings of
seven-level systems in a form of three-qubit or qubit-qutrit systems are
discussed. We use the three-qubit encoding of the system in order to
investigate subadditivity and strong subadditivity conditions for the thermal
state of the particle. The qubit-qutrit encoding is employed to suggest a
single qudit algorithm for calculation of parity of a bit string. Obtained
results indicate on the potential resource of multilevel systems for
realization of quantum information processing.Comment: 6 pages, 3 figures; published versio
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