214 research outputs found
La llum, vista a través de l'electrodinà mica quà ntica
El premi Nobel de fĂsica del 2005 es va concedir a tres investigadors en el camp de l'òptica quĂ ntica. És sorprenent el que actualment s'arriba a fer amb la llum, treballant en l'Ă mbit de l'electrodinĂ mica quĂ ntica
Adiabatic Splitting, Transport, and Self-Trapping of a Bose-Einstein Condensate in a Double-Well Potential
We show that the adiabatic dynamics of a Bose-Einstein condensate (BEC) in a
double well potential can be described in terms of a dark variable resulting
from the combination of the population imbalance and the spatial atomic
coherence between the two wells. By means of this dark variable, we extend, to
the non-linear matter wave case, the recent proposal by Vitanov and Shore
[Phys. Rev. A 73, 053402 (2006)] on adiabatic passage techniques to coherently
control the population of two internal levels of an atom/molecule. We
investigate the conditions to adiabatically split or transport a BEC as well as
to prepare an adiabatic self trapping state by the optimal delayed temporal
variation of the tunneling rate via either the energy bias between the two
wells or the BEC non-linearity. The emergence of non-linear eigenstates and
unstable stationary solutions of the system as well as their role in the
breaking down of the adiabatic dynamics is investigated in detail.Comment: 8 pages, 7 figure
Double barrier potentials for matter-wave gap solitons
We investigate collisions of solitons of the gap type, supported by a lattice
potential in repulsive Bose-Einstein condensates, with an effective
double-barrier potential that resembles a Fabry-Perot cavity. We identify
conditions under which the trapping of the entire incident soliton in the
cavity is possible. Collisions of the incident soliton with an earlier trapped
one are considered too. In the latter case, many outcomes of the collisions are
identified, including merging, release of the trapped soliton with or without
being replaced by the incoming one, and trapping of both solitons.Comment: 5 pages, 4 figure
Full polarization chaos in a pump-polarization modulated isotropic cavity laser
We study the dynamic behavior of an optically pumped J = 0 → J = 1 → J = 0 laser operating with an isotropic ring cavity and a linearly polarized pump field whose direction of polarization is modulated by the sinusoidal law θ(t) = m sin Ωt. Modulation frequencies Ω of the same order of magnitude as the transverse relaxation rate of the laser transition are considered here. At large enough modulation amplitudes, and for a detuned cavity, we obtain fully developed polarization chaos, which affects both the ellipticity and the orientation of the polarization ellipse as well as the laser intensity
A deterministic cavity-QED source of polarization entangled photon pairs
We present two cavity quantum electrodynamics proposals that, sharing the
same basic elements, allow for the deterministic generation of entangled
photons pairs by means of a three-level atom successively coupled to two single
longitudinal mode high-Q optical resonators presenting polarization degeneracy.
In the faster proposal, the three-level atom yields a polarization entangled
photon pair via two truncated Rabi oscillations, whereas in the adiabatic
proposal a counterintuitive Stimulated Raman Adiabatic Passage process is
considered. Although slower than the former process, this second method is very
efficient and robust under fluctuations of the experimental parameters and,
particularly interesting, almost completely insensitive to atomic decay.Comment: 5 pages, 5 figure
Filtering of matter wave vibrational states via spatial adiabatic passage
We discuss the filtering of the vibrational states of a cold atom in an
optical trap, by chaining this trap with two empty ones and controlling
adiabatically the tunneling. Matter wave filtering is performed by selectively
transferring the population of the highest populated vibrational state to the
most distant trap while the population of the rest of the states remains in the
initial trap. Analytical conditions for two-state filtering are derived and
then applied to an arbitrary number of populated bound states. Realistic
numerical simulations close to state-of-the-art experimental arrangements are
performed by modeling the triple well with time dependent P\"oschl-Teller
potentials. In addition to filtering of vibrational states, we discuss
applications for quantum tomography of the initial population distribution and
engineering of atomic Fock states that, eventually, could be used for tunneling
assisted evaporative cooling.Comment: 7 pages, 6 figure
Experimental observation of parametric effects near period doubling in a loss-modulated CO2 laser
A number of parametric effects, such as suppression of period doubling, shift of the bifurcation point, scaling law relating the shift and the perturbation amplitude, influence of the detuning on the suppression, reaching of the maximum gain between the original and shifted bifurcation points, and scaling law for idler power are experimentally observed near period doubling bifurcation in a loss-driven CO2 laser that is subjected to periodic loss perturbations at a frequency that is close to a parametric resonance of the unperturbed system
Generation of entangled photon pairs in optical cavity-QED: Operating in the bad cavity limit
We propose an optical cavity-QED scheme for the deterministic generation of
polarization entangled photon pairs that operates with high fidelity even in
the bad cavity limit. The scheme is based on the interaction of an excited
four-level atom with two empty optical cavity modes via an adiabatic passage
process. Monte-Carlo wave function simulations are used to evaluate the
fidelity of the cavity-QED source and its entanglement capability in the
presence of decoherence. In the bad cavity limit, fidelities close to one are
predicted for state-of-the-art experimental parameter values.Comment: 9 pages and 5 figure
Saturation spectroscopy in optically thick three-level gas media
High-contrast transmission spectra arising from saturated absorption in optically thick Doppler-broadened three-level media are analyzed within the formalism of Maxwell-Bloch-type equations. It is found that although in the strong pumping engine propagation-induced line narrowing and light-shift elimination occur, spectral features lying within the natural linewidth cannot be resolved
Generalized Einstein B coefficients for coherently driven three-level systems
Generalized Einstein B coefficients for coherently driven closed three-level systems are introduced by means of the quantum-jump technique. The nonreciprocity between stimulated emission and absorption for both one-photon and two-photon gain and loss processes has been studied and quantified in terms of the rates of the particular incoherent processes present in each three-level system. Some general properties of these generalized Einstein B coefficients have been found. In particular, whenever the generalized Einstein B coefficient for one-photon gain overcomes that for one-photon loss then the generalized Einstein B coefficient for two-photon loss overcomes that for two-photon gain, and vice versa. Finally, we have obtained simple analytical expressions indicating the way to maximize the asymmetry between stimulated emission and absorption coefficients either for one-photon or for two-photon processes
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