2,933 research outputs found
Quantum phase space picture of Bose-Einstein Condensates in a double well: Proposals for creating macroscopic quantum superposition states and a study of quantum chaos
We present a quantum phase space model of Bose-Einstein condensate (BEC) in a
double well potential. In a two-mode Fock-state analysis we examine the
eigenvectors and eigenvalues and find that the energy correlation diagram
indicates a transition from a delocalized to a fragmented regime. Phase space
information is extracted from the stationary quantum states using the Husimi
distribution function. It is shown that the quantum states are localized on the
known classical phase space orbits of a nonrigid physical pendulum, and thus
the novel phase space characteristics of a nonrigid physical pendulum such as
the motions are seen to be a property of the exact quantum states. Low
lying states are harmonic oscillator like libration states while the higher
lying states are Schr\"odinger cat-like superpositions of two pendulum rotor
states. To study the dynamics in phase space, a comparison is made between a
displaced quantum wavepacket and the trajectories of a swarm of points in
classical phase space. For a driven double well, it is shown that the classical
chaotic dynamics is manifest in the dynamics of the quantum states pictured
using the Husimi distribution. Phase space analogy also suggests that a
phase displaced wavepacket put on the unstable fixed point on a separatrix will
bifurcate to create a superposition of two pendulum rotor states - a
Schr\"odinger cat state (number entangled state) for BEC. It is shown that the
choice of initial barrier height and ramping, following a phase
imprinting on the condensate, can be used to generate controlled entangled
number states with tunable extremity and sharpness.Comment: revised version, 13 pages, 13 figure
Localized Asymmetric Atomic Matter Waves in Two-Component Bose-Einstein Condensates Coupled with Two Photon Microwave Field
We investigate localized atomic matter waves in two-component Bose-Einstein
condensates coupled by the two photon microwave field. Interestingly, the
oscillations of localized atomic matter waves will gradually decay and finally
become non-oscillating behavior even if existing coupling field. In particular,
atom numbers occupied in two different hyperfine spin states will appear
asymmetric occupations after some time evolution.Comment: 4 pages, 4 figure
Dynamical studies of macroscopic superposition states: Phase engineering of controlled entangled number states of Bose-Einstein condensate in multiple wells
We provide a scheme for the generation of entangled number states of
Bose-Einstein condensates in multiple wells with cyclic pairwise connectivity.
The condensate ground state in a multiple well trap can self-evolve, when phase
engineered with specific initial phase differences between the neighboring
wells, to a macroscopic superposition state with controllable entanglement --
to multiple well generalization of double well NOON states. We demonstrate
through numerical simulations the creation of entangled states in three and
four wells and then explore the creation of "larger" entangled states where
there are either a larger number of particles in each well or a larger number
of wells. The type of entanglement produced as the particle numbers, or
interaction strength, increases changes in a novel and initially unexpected
manner.Comment: 13 pages, 14 figure
Multiconfigurational Hartree-Fock theory for identical bosons in a double well
Multiconfigurational Hartree-Fock theory is presented and implemented in an
investigation of the fragmentation of a Bose-Einstein condensate made of
identical bosonic atoms in a double well potential at zero temperature. The
approach builds in the effects of the condensate mean field and of atomic
correlations by describing generalized many-body states that are composed of
multiple configurations which incorporate atomic interactions. Nonlinear and
linear optimization is utilized in conjunction with the variational and
Hylleraas-Undheim theorems to find the optimal ground and excited states of the
interacting system. The resulting energy spectrum and associated eigenstates
are presented as a function of double well barrier height. Delocalized and
localized single configurational states are found in the extreme limits of the
simple and fragmented condensate ground states, while multiconfigurational
states and macroscopic quantum superposition states are revealed throughout the
full extent of barrier heights. Comparison is made to existing theories that
either neglect mean field or correlation effects and it is found that
contributions from both interactions are essential in order to obtain a robust
microscopic understanding of the condensate's atomic structure throughout the
fragmentation process.Comment: 21 pages, 13 figure
The structure of the QED-Vacuum and Electron-Positron Pair Production in Super-Intense, pulsed Laser Fields
We discuss electron-positron pair-production by super-intense, short laser
pulses off the physical vacuum state locally deformed by (stripped) nuclei with
large nuclear charges. Consequences of non-perturbative vacuum polarisation
resulting from such a deformation are shortly broached. Production
probabilities per pulse are calculated.Comment: 10 pages, 1 figure, submitted to Journal of Physics
Generating ring currents, solitons, and svortices by stirring a Bose-Einstein condensate in a toroidal trap
We propose a simple stirring experiment to generate quantized ring currents
and solitary excitations in Bose-Einstein condensates in a toroidal trap
geometry. Simulations of the 3D Gross-Pitaevskii equation show that pure ring
current states can be generated efficiently by adiabatic manipulation of the
condensate, which can be realized on experimental time scales. This is
illustrated by simulated generation of a ring current with winding number two.
While solitons can be generated in quasi-1D tori, we show the even more robust
generation of hybrid, solitonic vortices (svortices) in a regime of wider
confinement. Svortices are vortices confined to essentially one-dimensional
dynamics, which obey a similar phase-offset--velocity relationship as solitons.
Marking the transition between solitons and vortices, svortices are a distinct
class of symmetry-breaking stationary and uniformly rotating excited solutions
of the 2D and 3D Gross-Pitaevskii equation in a toroidal trapping potential.
Svortices should be observable in dilute-gas experiments.Comment: 8 pages, 4 figures; accepted for publication in J. Phys. B (Letters
Modulational Instability and Complex Dynamics of Confined Matter-Wave Solitons
We study the formation of bright solitons in a Bose-Einstein condensate of
Li atoms induced by a sudden change in the sign of the scattering length
from positive to negative, as reported in a recent experiment (Nature {\bf
417}, 150 (2002)). The numerical simulations are performed by using the 3D
Gross-Pitaevskii equation (GPE) with a dissipative three-body term. We show
that a number of bright solitons is produced and this can be interpreted in
terms of the modulational instability of the time-dependent macroscopic wave
function of the Bose condensate. In particular, we derive a simple formula for
the number of solitons that is in good agreement with the numerical results of
3D GPE. By investigating the long time evolution of the soliton train solving
the 1D GPE with three-body dissipation we find that adjacent solitons repel
each other due to their phase difference. In addition, we find that during the
motion of the soliton train in an axial harmonic potential the number of
solitonic peaks changes in time and the density of individual peaks shows an
intermittent behavior. Such a complex dynamics explains the ``missing
solitons'' frequently found in the experiment.Comment: to be published in Phys. Rev. Let
Nanosecond time transfer via shuttle laser ranging experiment
A method is described to use a proposed shuttle laser ranging experiment to transfer time with nanosecond precision. All that need be added to the original experiment are low cost ground stations and an atomic clock on the shuttle. It is shown that global time transfer can be accomplished with 1 ns precision and transfer up to distances of 2000 km can be accomplished with better than 100 ps precision
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