14,794 research outputs found
Atomic coherence and interference phenomena in resonant nonlinear optical interactions
Interference effects in quantum transitions, giving rise to amplification
without inversion, optical transparency and to enhancements in nonlinear
optical frequency conversions are considered. Review of the relevant early
theoretical and experimental results is given. The role of relaxation
processes, spontaneous cascade of polarizations, local field effects,
Doppler-broadening, as well as specific features of the interference in the
spectral continuum are discussed.Comment: 13 pages, 13 eps figures, review paper, Proceedings of the 15th
International Conference on Nonlinear Optics - ICONO'9
Enhanced four-wave mixing via elimination of inhomogeneous broadening by coherent driving of quantum transition with control fields
We show that atoms from wide velocity interval can be concurrently involved
in Doppler-free two-photon resonant far from frequency degenerate four-wave
mixing with the aid of auxiliary electromagnetic field. This gives rise to
substantial enhancement of the output radiation generated in optically thick
medium. Numerical illustrations addressed to typical experimental conditions
are given.Comment: LaTeX2e, hyperref, 7 pages, 5 figures, to appear in PRA 1 august 200
Schwinger Pair Creation of Particles and Strings
I shortly review the worldline instanton method for calculating Schwinger
pair production rates in (i) one-loop QED (ii) multiloop QED and (iii) one-loop
open string theory.Comment: 8 pages, 3 figures, talk given at XIV Mexican School of Particles and
Fields, November 8 - 12, 2010, Morelia, Mexico, to appear in the conference
proceeding
Electron-Positron Pair Production in Space- or Time-Dependent Electric Fields
Treating the production of electron and positron pairs by a strong electric
field from the vacuum as a quantum tunneling process we derive, in
semiclassical approximation, a general expression for the pair production rate
in a -dependent electric field pointing in the -direction. We also
allow for a smoothly varying magnetic field parallel to . The result is
applied to a confined field for , a
semi-confined field for , and a linearly increasing
field . The boundary effects of the confined fields on
pair-production rates are exhibited. A simple variable change in all formulas
leads to results for electric fields depending on time rather than space.
In addition, we discuss tunneling processes in which empty atomic bound
states are spontaneously filled by negative-energy electrons from the vacuum
under positron emission. In particular, we calculate the rate at which the
atomic levels of a bare nucleus of finite size and large
are filled by spontaneous pair creation.Comment: 33 pages and 9 figures. to appear in Phys. Rev.
Manifestation of spin-orbit interaction in tunneling between 2D electron layers
An influence of spin-orbit interaction on the tunneling between two 2D
electron layers is considered. Particular attention is addressed to the
relation between the contribution of Rashba and Dresselhaus types. It is shown
that without scattering of the electrons, the tunneling conductance can either
exhibit resonances at certain voltage values or be substantially suppressed
over the whole voltage range. The dependence of the conductance on voltage
turns out to be very sensitive to the relation between Rashba and Dresselhaus
contributions even in the absence of magnetic field. The elastic scattering
broadens the resonances in the first case and restores the conductance to a
larger magnitude in the latter one. These effects open possibility to determine
the parameters of spin-orbit interaction and electrons scattering time in
tunneling experiments with no necessity of external magnetic field
A young contracting white dwarf in the peculiar binary HD 49798/RX J0648.0--4418?
HD 49798/RX J0648.0--4418 is a peculiar X-ray binary with a hot subdwarf
(sdO) mass donor. The nature of the accreting compact object is not known, but
its spin period ~s and s~s, prove
that it can be only either a white dwarf or a neutron star. The spin-up has
been very stable for more than 20 years. We demonstrate that the continuous
stable spin-up of the compact companion of HD 49798 can be best explained by
contraction of a young white dwarf with an age ~Myrs. This allows us to
interpret all the basic parameters of the system in the framework of an
accreting white dwarf. We present examples of binary evolution which result in
such systems. If correct, this is the first direct evidence for a white dwarf
contraction on early evolutionary stages.Comment: 9 pages, accepted to MNRA
The Zel'dovich effect and evolution of atomic Rydberg spectra along the Periodic Table
In 1959 Ya. B. Zel'dovich predicted that the bound-state spectrum of the
non-relativistic Coulomb problem distorted at small distances by a short-range
potential undergoes a peculiar reconstruction whenever this potential alone
supports a low-energy scattering resonance. However documented experimental
evidence of this effect has been lacking. Previous theoretical studies of this
phenomenon were confined to the regime where the range of the short-ranged
potential is much smaller than Bohr's radius of the Coulomb field. We go beyond
this limitation by restricting ourselves to highly-excited s states. This
allows us to demonstrate that along the Periodic Table of elements the
Zel'dovich effect manifests itself as systematic periodic variation of the
Rydberg spectra with a period proportional to the cubic root of the atomic
number. This dependence, which is supported by analysis of experimental and
numerical data, has its origin in the binding properties of the ionic core of
the atom.Comment: 17 pages, 12 figure
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