448 research outputs found
Single photons on demand from 3D photonic band-gap structures
We describe a practical implementation of a (semi-deterministic) photon gun
based on stimulated Raman adiabatic passage pumping and the strong enhancement
of the photonic density of states in a photonic band-gap material. We show that
this device allows {\em deterministic} and {\em unidirectional} production of
single photons with a high repetition rate of the order of 100kHz. We also
discuss specific 3D photonic microstructure architectures in which our model
can be realized and the feasibility of implementing such a device using
ions that produce single photons at the telecommunication
wavelength of m.Comment: 4 pages, 4 EPS figure
Effect of electron-electron interaction on the phonon-mediated spin relaxation in quantum dots
We estimate the spin relaxation rate due to spin-orbit coupling and acoustic
phonon scattering in weakly-confined quantum dots with up to five interacting
electrons. The Full Configuration Interaction approach is used to account for
the inter-electron repulsion, and Rashba and Dresselhaus spin-orbit couplings
are exactly diagonalized. We show that electron-electron interaction strongly
affects spin-orbit admixture in the sample. Consequently, relaxation rates
strongly depend on the number of carriers confined in the dot. We identify the
mechanisms which may lead to improved spin stability in few electron (>2)
quantum dots as compared to the usual one and two electron devices. Finally, we
discuss recent experiments on triplet-singlet transitions in GaAs dots subject
to external magnetic fields. Our simulations are in good agreement with the
experimental findings, and support the interpretation of the observed spin
relaxation as being due to spin-orbit coupling assisted by acoustic phonon
emission.Comment: 12 pages, 10 figures. Revised version. Changes in section V
(simulation of PRL 98, 126601 experiment
Self-optimization of optical confinement in ultraviolet photonic crystal slab laser
We studied numerically and experimentally the effects of structural disorder
on the performance of ultraviolet photonic crystal slab lasers. Optical gain
selectively amplifies the high-quality modes of the passive system. For these
modes, the in-plane and out-of-plane leakage rates may be automatically
balanced in the presence of disorder. The spontaneous optimization of in-plane
and out-of-plane confinement of light in a photonic crystal slab may lead to a
reduction of the lasing threshold.Comment: 5 pages, 5 figure
ASPECTS REGARDING THE APPEARANCE AND THE EVOLUTION OF KEYNESIAN DOCTRINE
This present paper is based on the importance of the keynesian doctrine in time and tries to make a brief foray into the life and work of John Maynard Keynes, revealing important aspects related to the new concepts this doctrine brought in the history of economic thought, looking at the same time to the criticism addressed to the keynesism and studying the effects they had in the development study of economic science. The objective of this theory is “the analysis of the mechanism of the market economy in order to ensure sustainable development, reducing or eliminating the disequilibrium, when it is not verified in practice the idea of the self equilibrium through the price mechanism."Keynes wrote in an era marked by mass unemployment, by degradation and suffering at an incredible level. A reasonable person could have supported the failure of capitalism, concluding that only major institutional changes - perhaps nationalization of means of production - could restore economic health
Switchable lasing in coupled multimode microcavities
We propose the new concept of a switchable multimode microlaser. As a
generic, realistic model of a multimode microresonator a system of two coupled
defects in a two-dimensional photonic crystal is considered. We demonstrate
theoretically that lasing of the cavity into one selected resonator mode can be
caused by injecting an appropriate optical pulse at the onset of laser action
(injection seeding). Temporal mode-to-mode switching by re-seeding the cavity
after a short cool-down period is demonstrated by direct numerical solution. A
qualitative analytical explanation of the mode switching in terms of the laser
bistability is presented.Comment: Accepted for publication in Physical Review Letters. Published,
somewhat shortened versio
Coherent spin dynamics in quantum wells in quantizing magnetic field
We investigate theoretically the coherent longitudinal and transversal spin
relaxation of photoexcited electrons in quantum wells in quantized magnetic
fields. We find the relaxation time for typical quantum well parameters between
100 and 1000 ps. For a realistic random potential the relaxation process
depends on the electron energy and g-factor, demonstrating oscillations in the
spin polarization accompanying the spin relaxation. The dependence of spin
relaxation on applied field, and thus on the corresponding "magnetic" length,
can be used to characterize the spatial scale of disorder in quantum wells.Comment: 13 pages, 4 figure
Microscopic derivation of the Jaynes-Cummings model with cavity losses
In this paper we provide a microscopic derivation of the master equation for
the Jaynes-Cummings model with cavity losses. We single out both the
differences with the phenomenological master equation used in the literature
and the approximations under which the phenomenological model correctly
describes the dynamics of the atom-cavity system. Some examples wherein the
phenomenological and the microscopic master equations give rise to different
predictions are discussed in detail.Comment: 9 pages, 3 figures New version with minor correction Accepted for
publication on Physical Review
Quantitative analysis of several random lasers
We prescribe the minimal set of experimental data and parameters that should
be reported for random-laser experiments and models. This prescript allows for
a quantitative comparison between different experiments, and for a criterion
whether a model predicts the outcome of an experiment correctly. In none of
more than 150 papers on random lasers that we found these requirements were
fulfilled. We have nevertheless been able to analyze a number of published
experimental results and recent experiments of our own. Using our method we
determined that the most intriguing property of the random laser (spikes) is in
fact remarkably similar for different random lasers.Comment: 3 pages, 1 figur
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