61 research outputs found
Pulsed squeezed light: simultaneous squeezing of multiple modes
We analyze the spectral properties of squeezed light produced by means of
pulsed, single-pass degenerate parametric down-conversion. The multimode output
of this process can be decomposed into characteristic modes undergoing
independent squeezing evolution akin to the Schmidt decomposition of the
biphoton spectrum. The main features of this decomposition can be understood
using a simple analytical model developed in the perturbative regime. In the
strong pumping regime, for which the perturbative approach is not valid, we
present a numerical analysis, specializing to the case of one-dimensional
propagation in a beta-barium borate waveguide. Characterization of the
squeezing modes provides us with an insight necessary for optimizing homodyne
detection of squeezing. For a weak parametric process, efficient squeezing is
found in a broad range of local oscillator modes, whereas the intense
generation regime places much more stringent conditions on the local
oscillator. We point out that without meeting these conditions, the detected
squeezing can actually diminish with the increasing pumping strength, and we
expose physical reasons behind this inefficiency
Multimode Squeezing Properties of a Confocal Opo: Beyond the Thin Crystal Approximation
Up to now, transverse quantum effects (usually labelled as "quantum imaging"
effects) which are generated by nonlinear devices inserted in resonant optical
cavities have been calculated using the "thin crystal approximation", i.e.
taking into account the effect of diffraction only inside the empty part of the
cavity, and neglecting its effect in the nonlinear propagation inside the
nonlinear crystal. We introduce in the present paper a theoretical method which
is not restricted by this approximation. It allows us in particular to treat
configurations closer to the actual experimental ones, where the crystal length
is comparable to the Rayleigh length of the cavity mode. We use this method in
the case of the confocal OPO, where the thin crystal approximation predicts
perfect squeezing on any area of the transverse plane, whatever its size and
shape. We find that there exists in this case a "coherence length" which gives
the minimum size of a detector on which perfect squeezing can be observed, and
which gives therefore a limit to the improvement of optical resolution that can
be obtained using such devices.Comment: soumis le 04.03.2005 a PR
Spatial patterns in optical parametric oscillators with spherical mirrors: classical and quantum effects: errata
We investigate the formation of transverse patterns in a doubly resonant degenerate optical parametric oscillator. Extending previous work, we treat the more realistic case of a spherical mirror cavity with a finite-sized input pump field. Using numerical simulations in real space, we determine the conditions on the cavity geometry, pump size and detunings for which pattern formation occurs; we find multistability of different types of optical patterns. Below threshold, we analyze the dependence of the quantum image on the width of the input field, in the near and in the far field
Brillouin propagation modes in optical lattices: Interpretation in terms of nonconventional stochastic resonance
We report the first direct observation of Brillouin-like propagation modes in a dissipative periodic optical lattice. This has been done by observing a resonant behavior of the spatial diffusion coefficient in the direction corresponding to the propagation mode with the phase velocity of the moving intensity modulation used to excite these propagation modes. Furthermore, we show theoretically that the amplitude of the Brillouin mode is a nonmonotonic function of the strength of the noise corresponding to the optical pumping, and discuss this behavior in terms of nonconventional stochastic resonance
Spinor Bosonic Atoms in Optical Lattices: Symmetry Breaking and Fractionalization
We study superfluid and Mott insulator phases of cold spin-1 Bose atoms with
antiferromagnetic interactions in an optical lattice, including a usual polar
condensate phase, a condensate of singlet pairs, a crystal spin nematic phase,
and a spin singlet crystal phase. We suggest a possibility of exotic
fractionalized phases of spinor BEC and discuss them in the language of
topological defect condensation and lattice gauge theory.Comment: 4 pages, 1 figure included; references adde
Enhanced bioremediation of n-alkane in petroleum sludge using bacterial consortium amended with rhamnolipid and micronutrients
Atomic collision dynamics in optical lattices
We simulate collisions between two atoms, which move in an optical lattice
under the dipole-dipole interaction. The model describes simultaneously the two
basic dynamical processes, namely the Sisyphus cooling of single atoms, and the
light-induced inelastic collisions between them. We consider the J=1/2 -> J=3/2
laser cooling transition for Cs, Rb and Na. We find that the hotter atoms in a
thermal sample are selectively lost or heated by the collisions, which modifies
the steady state distribution of atomic velocities, reminiscent of the
evaporative cooling process.Comment: 17 pages, 15 figure
Cold bosonic atoms in optical lattices
The dynamics of an ultracold dilute gas of bosonic atoms in an optical
lattice can be described by a Bose-Hubbard model where the system parameters
are controlled by laser light. We study the continuous (zero temperature)
quantum phase transition from the superfluid to the Mott insulator phase
induced by varying the depth of the optical potential, where the Mott insulator
phase corresponds to a commensurate filling of the lattice (``optical
crystal''). Examples for formation of Mott structures in optical lattices with
a superimposed harmonic trap, and in optical superlattices are presented.Comment: 4 pages 4 figures New: added references; Postscript version available
at:
http://th-physics.uibk.ac.at/zoller/Publications/PZListOfPublications.htm
Relationship between default mode network and resting-state electroencephalographic alpha rhythms in cognitively unimpaired seniors and patients with dementia due to alzheimerâs disease
Localized breathing solutions for Bose-Einstein condensates in periodic traps
We demonstrate the existence of localized oscillatory breathers for
quasi-one-dimensional Bose-Einstein condensates confined in periodic
potentials. The breathing behavior corresponds to position-oscillations of
individual condensates about the minima of the potential lattice. We deduce the
structural stability of the localized oscillations from the construction. The
stability is confirmed numerically for perturbations to the initial state of
the condensate, to the potential trap, as well as for external noise. We also
construct periodic and chaotic extended oscillations for the chain of
condensates. All our findings are verified by direct numerical integration of
the Gross-Pitaevskii equation in one dimension.Comment: LaTeX, 6 pages, 7 postscript figures, extended version of previous
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