1,127 research outputs found
Reentrant transition of bosons in a quasiperiodic potential
We investigate the behavior of a two dimensional array of Bose-Einstein
condensate tubes described by means of a Bose-Hubbard Hamiltonian. Using a
Wannier function expansion for the wavefunction in each tube, we compute the
Bose-Hubbard parameters related to two different longitudinal potentials,
periodic and quasiperiodic. We predict that - upon increasing the external
potential strength along the direction of the tubes - the condensate can
experience a reentrant transition between a Mott insulating phase and the
superfluid one.Comment: Accepted for publication in EP
Radiative collisional heating at the Doppler limit for laser-cooled magnesium atoms
We report Monte Carlo wave function simulation results on cold collisions
between magnesium atoms in a strong red-detuned laser field. This is the normal
situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate
due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical
trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We
find that radiative heating does not seem to affect the Doppler limit in this
case. We also describe a channelling mechanism due to the missing Q branch in
the excitation scheme, which could lead to a suppression of inelastic
collisions, and find that this mechanism is not present in our simulation
results due to the multistate character of the excitation process.Comment: 4 pages, RevTeX 4; v2 contains minor revisions based on referee
comments (5 pages
Turbulence in Binary Bose-Einstein Condensates Generated by Highly Non-Linear Rayleigh-Taylor and Kelvin-Helmholtz Instabilities
Quantum turbulence (QT) generated by the Rayleigh-Taylor instability in
binary immiscible ultracold 87Rb atoms at zero temperature is studied
theoretically. We show that the quantum vortex tangle is qualitatively
different from previously considered superfluids, which reveals deep relations
between QT and classical turbulence. The present QT may be generated at
arbitrarily small Mach numbers, which is a unique property not found in
previously studied superfluids. By numerical solution of the coupled
Gross-Pitaevskii equations we find that the Kolmogorov scaling law holds for
the incompressible kinetic energy. We demonstrate that the phenomenon may be
observed in the laboratory.Comment: Revised version. 7 pages, 8 figure
Stability of the solutions of the Gross-Pitaevskii equation
We examine the static and dynamic stability of the solutions of the
Gross-Pitaevskii equation and demonstrate the intimate connection between them.
All salient features related to dynamic stability are reflected systematically
in static properties. We find, for example, the obvious result that static
stability always implies dynamic stability and present a simple explanation of
the fact that dynamic stability can exist even in the presence of static
instability.Comment: 7 pages, 1 figur
Phases of a rotating Bose-Einstein condensate with anharmonic confinement
We examine an effectively repulsive Bose-Einstein condensate of atoms that
rotates in a quadratic-plus-quartic potential. With use of a variational method
we identify the three possible phases of the system (multiple quantization,
single quantization, and a mixed phase) as a function of the rotational
frequency of the gas and of the coupling constant. The derived phase diagram is
shown to be universal and the continuous transitions to be exact in the limit
of weak coupling and small anharmonicity. The variational results are found to
be consistent with numerical solutions of the Gross-Pitaevskii equation.Comment: 8 pages, 6 figure
Center of mass rotation and vortices in an attractive Bose gas
The rotational properties of an attractively interacting Bose gas are studied
using analytical and numerical methods. We study perturbatively the ground
state phase space for weak interactions, and find that in an anharmonic trap
the rotational ground states are vortex or center of mass rotational states;
the crossover line separating these two phases is calculated. We further show
that the Gross-Pitaevskii equation is a valid description of such a gas in the
rotating frame and calculate numerically the phase space structure using this
equation. It is found that the transition between vortex and center of mass
rotation is gradual; furthermore the perturbative approach is valid only in an
exceedingly small portion of phase space. We also present an intuitive picture
of the physics involved in terms of correlated successive measurements for the
center of mass state.Comment: version2, 17 pages, 5 figures (3 eps and 2 jpg
Using operational scenarios in a virtual reality enhanced design process
Maritime user interfaces for ships’ bridges are highly dependent on the context in which they are used, and rich maritime context is difficult to recreate in the early stages of user-centered design processes. Operations in Arctic waters where crews are faced with extreme environmental conditions, technology limitations and a lack of accurate navigational information further increase this challenge. There is a lack of research supporting the user-centered design of workplaces for hazardous Arctic operations. To meet this challenge, this paper reports on the process of developing virtual reality-reconstructed operational scenarios to connect stakeholders, end-users, designers, and human factors specialists in a joint process. This paper explores how virtual reality-reconstructed operational scenarios can be used as a tool both for concept development and user testing. Three operational scenarios were developed, implemented in a full mission bridge simulator, recreated in virtual reality (VR), and finally tested on navigators (end-users). Qualitative data were captured throughout the design process and user-testing, resulting in a thematic analysis that identified common themes reflecting the experiences gained throughout this process. In conclusion, we argue that operational scenarios, rendered in immersive media such as VR, may be an important and reusable asset when supporting maritime design processes and in maritime training and education
Multiply quantized vortices in trapped Bose-Einstein condensates
Vortex configurations in rotating Bose-Einstein condensed gases trapped in
power-law and anharmonic potentials are studied. When the confining potential
is steeper than harmonic in the plane perpendicular to the axis of rotation,
vortices with quantum numbers larger than one are energetically favorable if
the interaction is weak enough. Features of the wave function for small and
intermediate rotation frequencies are investigated numerically.Comment: 9 pages, 6 figures. Revised and extended article following referee
repor
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