80 research outputs found
Raman scattering of atoms from a quasi-condensate in a perturbative regime
It is demonstrated that measurements of positions of atoms scattered from a
quasi-condensate in a Raman process provide information on the temperature of
the parent cloud. In particular, the widths of the density and second order
correlation functions are sensitive to the phase fluctuations induced by
non-zero temperature of the quasi-condensate. It is also shown how these widths
evolve during expansion of the cloud of scattered atoms. These results are
useful for planning future Raman scattering experiments and indicate the degree
of spatial resolution of atom-position measurements necessary to detect the
temperature dependence of the quasi-condensate.Comment: 8 pages, 8 figure
Bogoliubov theory for atom scattering into separate regions
We review the Bogoliubov theory in the context of recent experiments, where
atoms are scattered from a Bose-Einstein Condensate into two well-separated
regions. We find the full dynamics of the pair-production process, calculate
the first and second order correlation functions and show that the system is
ideally number-squeezed. We calculate the Fisher information to show how the
entanglement between the atoms from the two regions changes in time. We also
provide a simple expression for the lower bound of the useful entanglement in
the system in terms of the average number of scattered atoms and the number of
modes they occupy. We then apply our theory to a recent "twin-beam" experiment
[R. B\"ucker {\it et al.}, Nat. Phys. {\bf 7}, 608 (2011)]. The only numerical
step of our semi-analytical description can be easily solved and does not
require implementation of any stochastic methods.Comment: 11 pages, 6 figure
Tradeoffs for number-squeezing in collisions of Bose-Einstein condensates
We investigate the factors that influence the usefulness of supersonic
collisions of Bose-Einstein condensates as a potential source of entangled
atomic pairs by analyzing the reduction of the number difference fluctuations
between regions of opposite momenta. We show that non-monochromaticity of the
mother clouds is typically the leading limitation on number squeezing, and that
the squeezing becomes less robust to this effect as the density of pairs grows.
We develop a simple model that explains the relationship between density
correlations and the number squeezing, allows one to estimate the squeezing
from properties of the correlation peaks, and shows how the multi-mode nature
of the scattering must be taken into account to understand the behavior of the
pairing. We analyze the impact of the Bose enhancement on the number squeezing,
by introducing a simplified low-gain model. We conclude that as far as
squeezing is concerned the preferable configuration occurs when atoms are
scattered not uniformly but rather into two well separated regions.Comment: 13 pages, 13 figures, final versio
Elastic scattering loss of atoms from colliding Bose-Einstein condensate wavepackets
Bragg diffraction of atoms by light waves has been used to create high
momentum components in a Bose-Einstein condensate. Collisions between atoms
from two distinct momentum wavepackets cause elastic scattering that can remove
a significant fraction of atoms from the wavepackets and cause the formation of
a spherical shell of scattered atoms. We develop a slowly varying envelope
technique that includes the effects of this loss on the condensate dynamics
described by the Gross-Pitaevski equation. Three-dimensional numerical
calculations are presented for two experimental situations: passage of a moving
daughter condensate through a non-moving parent condensate, and four-wave
mixing of matter waves.Comment: Phys. Rev. Lett, in pres
Improved Semiclassical Approximation for Bose-Einstein Condensates: Application to a BEC in an Optical Potential
We present semiclassical descriptions of Bose-Einstein condensates for
configurations with spatial symmetry, e.g., cylindrical symmetry, and without
any symmetry. The description of the cylindrical case is quasi-one-dimensional
(Q1D), in the sense that one only needs to solve an effective 1D nonlinear
Schrodinger equation, but the solution incorporates correct 3D aspects of the
problem. The solution in classically allowed regions is matched onto that in
classically forbidden regions by a connection formula that properly accounts
for the nonlinear mean-field interaction. Special cases for vortex solutions
are treated too. Comparisons of the Q1D solution with full 3D and Thomas-Fermi
ones are presented.Comment: 14 pages, 5 figure
Fully three dimensional breather solitons can be created using Feshbach resonance
We investigate the stability properties of breather solitons in a
three-dimensional Bose-Einstein Condensate with Feshbach Resonance Management
of the scattering length and con ned only by a one dimensional optical lattice.
We compare regions of stability in parameter space obtained from a fully 3D
analysis with those from a quasi two-dimensional treatment. For moderate con
nement we discover a new island of stability in the 3D case, not present in the
quasi 2D treatment. Stable solutions from this region have nontrivial dynamics
in the lattice direction, hence they describe fully 3D breather solitons. We
demonstrate these solutions in direct numerical simulations and outline a
possible way of creating robust 3D solitons in experiments in a Bose Einstein
Condensate in a one-dimensional lattice. We point other possible applications.Comment: 4 pages, 4 figures; accepted to Physical Review Letter
Few-cycle soliton propagation
Soliton propagation is usually described in the ``slowly varying envelope
approximation'' (SVEA) regime, which is not applicable for ultrashort pulses.
We present theoretical results and numerical simulations for both NLS and
parametric () ultrashort solitons in the ``generalised few-cycle
envelope approximation'' (GFEA) regime, demonstrating their altered
propagation.Comment: 4 pages, 4 figure
Stability of Waves in Multi-component DNLS system
In this work, we systematically generalize the Evans function methodology to
address vector systems of discrete equations. We physically motivate and
mathematically use as our case example a vector form of the discrete nonlinear
Schrodinger equation with both nonlinear and linear couplings between the
components. The Evans function allows us to qualitatively predict the stability
of the nonlinear waves under the relevant perturbations and to quantitatively
examine the dependence of the corresponding point spectrum eigenvalues on the
system parameters. These analytical predictions are subsequently corroborated
by numerical computations.Comment: to appear Journal of Physics A: Mathematical and Theoretica
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