309 research outputs found
Adiabatic population transfer in a three-level system driven by delayed laser pulses
We give a simple analytic solution that describes a novel method for population transfer in a three-level system driven by delayed pulses and which accounts for recent experimental results. This solution describes a procedure that is counter intuitive, and yet it is shown to be, in fact, one of the simplest solutions for multilevel systems arising from the adiabatic theorem. Its possible application to many-level systems is suggested
Studies of group velocity reduction and pulse regeneration with and without the adiabatic approximation
We present a detailed semiclassical study on the propagation of a pair of
optical fields in resonant media with and without adiabatic approximation. In
the case of near and on resonance excitation, we show detailed calculation,
both analytically and numerically, on the extremely slowly propagating probe
pulse and the subsequent regeneration of a pulse via a coupling laser. Further
discussions on the adiabatic approximation provide many subtle understandings
of the process including the effect on the band width of the regenerated
optical field. Indeed, all features of the optical pulse regeneration and most
of the intricate details of the process can be obtained with the present
treatment without invoke a full field theoretical method. For very far off
resonance excitation, we show that the analytical solution is nearly detuning
independent, a surprising result that is vigorously tested and compared to
numerical calculations with very good agreement.Comment: 13 pages, 15 figures, submitted to Phys. Rev.
Social determinants of content selection in the age of (mis)information
Despite the enthusiastic rhetoric about the so called \emph{collective
intelligence}, conspiracy theories -- e.g. global warming induced by chemtrails
or the link between vaccines and autism -- find on the Web a natural medium for
their dissemination. Users preferentially consume information according to
their system of beliefs and the strife within users of opposite narratives may
result in heated debates. In this work we provide a genuine example of
information consumption from a sample of 1.2 million of Facebook Italian users.
We show by means of a thorough quantitative analysis that information
supporting different worldviews -- i.e. scientific and conspiracist news -- are
consumed in a comparable way by their respective users. Moreover, we measure
the effect of the exposure to 4709 evidently false information (satirical
version of conspiracy theses) and to 4502 debunking memes (information aiming
at contrasting unsubstantiated rumors) of the most polarized users of
conspiracy claims. We find that either contrasting or teasing consumers of
conspiracy narratives increases their probability to interact again with
unsubstantiated rumors.Comment: misinformation, collective narratives, crowd dynamics, information
spreadin
Squeezing arbitrary cavity-field states through their interaction with a single driven atom
We propose an implementation of the parametric amplification of an arbitrary
radiation-field state previously prepared in a high-Q cavity. This nonlinear
process is accomplished through the dispersive interactions of a single
three-level atom (fundamental |g>, intermediate |i>, and excited |e> levels)
simultaneously with i) a classical driving field and ii) a previously prepared
cavity mode whose state we wish to squeeze. We show that, in the adiabatic
approximantion, the preparation of the initial atomic state in the intermediate
level |i> becomes crucial for obtaing the degenerated parametric amplification
process.Comment: Final published versio
Matched Pulse Propagation in a Three-Level System
The B\"{a}cklund transformation for the three-level Maxwell-Bloch equation is
presented in the matrix potential formalism. By applying the B\"{a}cklund
transformation to a constant electric field background, we obtain a general
solution for matched pulses (a pair of solitary waves) which can emit or absorb
a light velocity solitary pulse but otherwise propagate with their shapes
invariant. In the special case, this solution describes a steady state pulse
without emission or absorption, and becomes the matched pulse solution recently
obtained by Hioe and Grobe. A nonlinear superposition rule is derived from the
B\"{a}cklund transformation and used for the explicit construction of two
solitons as well as nonabelian breathers. Various new features of these
solutions are addressed. In particular, we analyze in detail the scattering of
"invertons", a specific pair of different wavelength solitons one of which
moving with the velocity of light. Unlike the usual case of soliton scattering,
the broader inverton changes its sign through the scattering. Surprisingly, the
light velocity inverton receives time advance through the scattering thereby
moving faster than light, which however does not violate causality.Comment: 20 pages, Latex, 12 eps figure files some comments and references are
added. postscript file with 12 figures can be obtained at
http://photon.kyunghee.ac.kr/~qhpark
Spatial evolution of short pulses under coherent population trapping
Spatial and temporal evolution is studied of two powerful short laser pulses
having different wavelengths and interacting with a dense three-level
Lambda-type optical medium under coherent population trapping. A general case
of unequal oscillator strengths of the transitions is considered. Durations of
the probe pulse and the coupling pulse () are assumed to be
shorter than any of the relevant atomic relaxation times. We propose analytical
and numerical solutions of a self-consistent set of coupled Schr\"{o}dinger
equations and reduced wave equations in the adiabatic limit with the account of
the first non-adiabatic correction. The adiabaticity criterion is also
discussed with the account of the pulse propagation. The dynamics of
propagation is found to be strongly dependent on the ratio of the transition
oscillator strengths. It is shown that envelopes of the pulses slightly change
throughout the medium length at the initial stage of propagation. This distance
can be large compared to the one-photon resonant absorption length. Eventually,
the probe pulse is completely reemitted into the coupling pulse during
propagation. The effect of localization of the atomic coherence has been
observed similar to the one predicted by Fleischhauer and Lukin (PRL, {\bf 84},
5094 (2000).Comment: 16 pages revtex style, 7 EPS figures, accepted to Physical Review
Preparation and control of a cavity-field state through atom-driven field interaction: towards long-lived mesoscopic states
The preparation of mesoscopic states of the radiation and matter fields
through atom-field interactions has been achieved in recent years and employed
for a range of striking applications in quantum optics. Here we present a
technique for the preparation and control of a cavity mode which, besides
interacting with a two-level atom, is simultaneously submitted to linear and
parametric amplification processes. The role of the amplification-controlling
fields in the achievement of real mesoscopic states, is to produce
highly-squeezed field states and, consequently, to increase both: i) the
distance in phase space between the components of the prepared superpositions
and ii) the mean photon number of such superpositions. When submitting the
squeezed superposition states to the action of similarly squeezed reservoirs,
we demonstrate that under specific conditions the decoherence time of the
states becomes independent of both the distance in phase space between their
components and their mean photon number. An explanation is presented to support
this remarkable result, together with a discussion on the experimental
implementation of our proposal. We also show how to produce number states with
fidelities higher than those derived as circular states
Diversity of hard-bottom fauna relative to environmental gradients in Kongsfjorden, Svalbard
A baseline study of hard-bottom zoobenthos in relation to environmental gradients in Kongsfjorden, a glacial fjord in Svalbard, is presented, based on collections from 1996 to 1998. The total species richness in 62 samples from 0 to 30 m depth along five transects was 403 species. Because 32 taxa could not be identified to species level and because 11 species are probably new to science, the total number of identified species was 360. Of these, 47 species are new for Svalbard waters. Bryozoa was the most diverse group. Biogeographic composition revealed features of both Arctic and sub-Arctic properties of the fauna. Species richness, frequency of species occurrence, mean abundance and biomass generally decreased towards the tidal glaciers in inner Kongsfjorden. Among eight environmental factors, depth was most important for explaining variance in the composition of the zoobenthos. The diversity was consistently low at shallow depths, whereas the non-linear patterns of species composition of deeper samples indicated a transitional zone between surface and deeper water masses at 15–20 m depth. Groups of “colonial” and “non-colonial” species differed in diversity, biogeographic composition and distribution by location and depth as well as in relation to other environmental factors. “Non-colonial” species made a greater contribution than “colonial” species to total species richness, total occurrence and biomass in samples, and were more influenced by the depth gradient. Biogeographic composition was sensitive to variation of zoobenthic characteristics over the studied depth range. A list of recorded species and a description of sampling sites are presented
Adiabatic population transfer via multiple intermediate states
This paper discusses a generalization of stimulated Raman adiabatic passage
(STIRAP) in which the single intermediate state is replaced by intermediate
states. Each of these states is connected to the initial state \state{i} with
a coupling proportional to the pump pulse and to the final state \state{f}
with a coupling proportional to the Stokes pulse, thus forming a parallel
multi- system. It is shown that the dark (trapped) state exists only
when the ratio between each pump coupling and the respective Stokes coupling is
the same for all intermediate states. We derive the conditions for existence of
a more general adiabatic-transfer state which includes transient contributions
from the intermediate states but still transfers the population from state
\state{i} to state \state{f} in the adiabatic limit. We present various
numerical examples for success and failure of multi- STIRAP which
illustrate the analytic predictions. Our results suggest that in the general
case of arbitrary couplings, it is most appropriate to tune the pump and Stokes
lasers either just below or just above all intermediate states.Comment: 14 pages, two-column revtex style, 10 figure
Theory of exciton-exciton correlation in nonlinear optical response
We present a systematic theory of Coulomb interaction effects in the
nonlinear optical processes in semiconductors using a perturbation series in
the exciting laser field. The third-order dynamical response consists of
phase-space filling correction, mean-field exciton-exciton interaction, and
two-exciton correlation effects expressed as a force-force correlation
function. The theory provides a unified description of effects of bound and
unbound biexcitons, including memory-effects beyond the Markovian
approximation. Approximations for the correlation function are presented.Comment: RevTex, 35 pages, 10 PostScript figs, shorter version submitted to
Physical Review
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