562 research outputs found
Classical versus quantum intensity-field correlations of scattered light from extended cold atomic clouds
We calculate the intensity-field correlations in the light scattered by N
cold atoms driven by a quasi-resonant laser field. Fundamental differences
occur if the atomic state is an entangled single-excitation state or a coherent
factorized state. We provide analytic expressions for the two-time field and
intensity correlation functions for the timed Dicke state and the quasi-Bloch
state. The comparison with multi-atom simulations shows good agreement between
numerical and analytic solutions.Comment: 15 pages, 5 figure
A quantum model for collective recoil lasing
Free Electron Laser (FEL) and Collective Atomic Recoil Laser (CARL) are
described by the same model of classical equations for properly defined scaled
variables. These equations are extended to the quantum domain describing the
particle's motion by a Schr\"{o}dinger equation coupled to a self-consistent
radiation field. The model depends on a single collective parameter
which represents the maximum number of photons emitted per particle. We
demonstrate that the classical model is recovered in the limit , in which the Wigner function associated to the Schr\"{o}dinger equation
obeys to the classical Vlasov equation. On the contrary, for ,
a new quantum regime is obtained in which both FELs and CARLs behave as a
two-state system coupled to the self-consistent radiation field and described
by Maxwell-Bloch equations
Cooperativity in light scattering by cold atoms
A cloud of cold N two-level atoms driven by a resonant laser beam shows
cooperative effects both in the scattered radiation field and in the radiation
pressure force acting on the cloud center-of-mass. The induced dipoles
synchronize and the scattered light presents superradiant and/or subradiant
features. We present a quantum description of the process in terms of a master
equation for the atomic density matrix in the scalar, Born-Markov
approximations, reduced to the single-excitation limit. From a perturbative
approach for weak incident field, we derive from the master equation the
effective Hamiltonian, valid in the linear regime. We discuss the validity of
the driven timed Dicke ansatz and of a partial wave expansion for different
optical thicknesses and we give analytical expressions for the scattered
intensity and the radiation pressure force on the center of mass. We also
derive an expression for collective suppression of the atomic excitation and
the scattered light by these correlated dipoles.Comment: 15 pages, 8 figure
The Semiclassical and Quantum Regimes of Superradiant Light Scattering from a Bose-Einstein Condensate
We show that many features of the recent experiments of Schneble et al. [D.
Schneble, Y. Torii, M. Boyd, E.W. Streed, D.E. Pritchard and W. Ketterle,
Science vol. 300, p. 475 (2003)], which demonstrate two different regimes of
light scattering by a Bose-Einstein condensate, can be described using a
one-dimensional mean-field quantum CARL model, where optical amplification
occurs simultaneously with the production of a periodic density modulation in
the atomic medium. The two regimes of light scattering observed in these
experiments, originally described as ``Kapiza-Dirac scattering'' and
``Superradiant Rayleigh scattering'', can be interpreted as the semiclassical
and quantum limits respectively of CARL lasing.Comment: 10 pages, 5 figures - to appear in Journal of Optics
Mean-Field Description of Cooperative Scattering by Atomic Clouds
We present analytic expressions for the scattering of light by an extended
atomic cloud. We obtain the solution for the mean-field excitation of different
atomic spherical distributions driven by an uniform laser, including the
initial build-up, the steady-state and the decay after the laser is switched
off. We show that the mean-field model does not describe subradiant scattering,
due to negative interference of the photons scattered by discrete atoms.Comment: 14 pages, 9 figure
Microscopic theory of photonic band gaps in optical lattices
We propose a microscopic model to describe the scattering of light by atoms
in optical lattices. The model is shown to efficiently capture Bragg
scattering, spontaneous emission and photonic band gaps. A connection to the
transfer matrix formalism is established in the limit of a one-dimensional
optical lattice, and we find the two theories to yield results in good
agreement. The advantage of the microscopic model is, however, that it suits
better for studies of finite-size and disorder effects.Comment: 5 pages, 6 figure
Quantum theory of SASE FEL
We describe a free-electron laser (FEL) in the Self-Amplified Spontaneous Emission (SASE) regime quantizing the electron motion and taking into account propagation effects. We demonstrate quantum purification of the SASE spectrum, i.e. in a properly defined quantum regime the spiking behavior disappears and the SASE power spectrum becomes very narrow
Radiation to atom quantum mapping by collective recoil in Bose-Einstein condensate
We propose an experiment to realize radiation to atom continuous variable
quantum mapping, i.e. to teleport the quantum state of a single mode radiation
field onto the collective state of atoms with a given momentum out of a
Bose-Einstein condensate. The atoms-radiation entanglement needed for the
teleportation protocol is established through the interaction of a single mode
with the condensate in presence of a strong far off-resonant pump laser,
whereas the coherent atomic displacement is obtained by the same interaction
with the radiation in a classical coherent field. In principle, verification of
the protocol requires a joint measurement on the recoiling atoms and the
condensate, however, a partial verification involving populations, i.e.
diagonal matrix elements may be obtained through counting atoms experiments
Atomic interaction effects in the superradiant light scattering from a Bose-Einstein condensate
We investigate the effects of the atomic interaction in the Superradiant
Rayleigh scattering from a Bose-Einstein condensate driven by a far-detuned
laser beam. We show that for a homogeneous atomic sample the atomic interaction
has only a dispersive effect, whereas in the inhomogeneous case it may increase
the decay of the matter-wave grating.Comment: 12 pages, 4 figures, presented to the XII International Laser Physics
Workshop, August 24-29, Hamburg, to be published in Laser Physic
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