2,116 research outputs found
Equilibrium vortex formation in ultrarapidly rotating two-component Bose-Einstein condensates
Equilibrium vortex formation in rotating binary Bose gases with a rotating
frequency higher than the harmonic trapping frequency is investigated
theoretically. We consider the system being evaporatively cooled to form
condensates and a combined numerical scheme is applied to ensure the binary
system being in an authentic equilibrium state. To keep the system stable
against the large centrifugal force of ultrafast rotation, a quartic trapping
potential is added to the existing harmonic part. Using the Thomas-Fermi
approximation, a critical rotating frequency \Omega_c is derived, which
characterizes the structure with or without a central density hole. Vortex
structures are studied in detail with rotation frequency both above and below
?\Omega_c and with respect to the miscible, symmetrically separated, and
asymmetrically separated phases in their nonrotating ground-state counterparts.Comment: 7 pages, 7 figure
Dynamical Equilibration Across a Quenched Phase Transition in a Trapped Quantum Gas
The formation of an equilibrium quantum state from an uncorrelated thermal
one through the dynamical crossing of a phase transition is a central question
of non-equilibrium many-body physics. During such crossing, the system breaks
its symmetry by establishing numerous uncorrelated regions separated by
spontaneously-generated defects, whose emergence obeys a universal scaling law
with the quench duration. Much less is known about the ensuing re-equilibrating
or "coarse-graining" stage, which is governed by the evolution and interactions
of such defects under system-specific and external constraints. In this work we
perform a detailed numerical characterization of the entire non-equilibrium
process, addressing subtle issues in condensate growth dynamics and
demonstrating the quench-induced decoupling of number and coherence growth
during the re-equilibration process. Our unique visualizations not only
reproduce experimental measurements in the relevant regimes, but also provide
valuable information in currently experimentally-inaccessible regimes.Comment: Supplementary Movie Previes: SM-Movie-1: https://youtu.be/3q7-CvuBylg
SM-Movie-2: https://youtu.be/-Gymaiv9rC0 SM-Movie-3:
https://youtu.be/w-O2SPiw3nE SM-Movie-4: https://youtu.be/P4xGyr4dwK
Dark pair coherent states of the motion of a trapped ion
We propose a scheme for generating vibrational pair coherent states of the
motion of an ion in a two-dimensional trap. In our scheme, the trapped ion is
excited bichromatically by three laser beams along different directions in the
X-Y plane of the ion trap. We show that if the initial vibrational state is
given by a two-mode Fock state, the final steady state, indicated by the
extinction of the fluorescence emitted by the ion, is a pure state. The
motional state of the ion in the equilibrium realizes that of the
highly-correlated pair coherent state.Comment: 14 pages, 3 figure
Bending-wave Instability of a Vortex Ring in a Trapped Bose-Einstein Condensate
Based on a velocity formula derived by matched asymptotic expansion, we
investigate the dynamics of a circular vortex ring in an axisymmetric
Bose-Einstein condensate in the Thomas-Fermi limit. The trajectory for an
axisymmetrically placed and oriented vortex ring is entirely determined,
revealing that the vortex ring generally precesses in condensate. The linear
instability due to bending waves is investigated both numerically and
analytically. General stability boundaries for various perturbed wavenumbers
are computed. In particular, the excitation spectrum and the absolutely stable
region for the static ring are analytically determined.Comment: 4 pages, 4 figure
Spontaneous Crystallization of Skyrmions and Fractional Vortices in the Fast-rotating and Rapidly-quenched Spin-1 Bose-Einstein Condensates
We investigate the spontaneous generation of crystallized topological defects
via the combining effects of fast rotation and rapid thermal quench on the
spin-1 Bose-Einstein condensates. By solving the stochastic projected
Gross-Pitaevskii equation, we show that, when the system reaches equilibrium, a
hexagonal lattice of skyrmions, and a square lattice of half-quantized vortices
can be formed in a ferromagnetic and antiferromagnetic spinor BEC, respetively,
which can be imaged by using the polarization-dependent phase-contrast method
Nonlinear Decoherence in Quantum State Preparation of a Trapped Ion
We present a nonlinear decoherence model which models decoherence effect
caused by various decohereing sources in a quantum system through a nonlinear
coupling between the system and its environment, and apply it to investigating
decoherence in nonclassical motional states of a single trapped ion. We obtain
an exactly analytic solution of the model and find very good agreement with
experimental results for the population decay rate of a single trapped ion
observed in the NIST experiments by Meekhof and coworkers (D. M. Meekhof, {\it
et al.}, Phys. Rev. Lett. {\bf 76}, 1796 (1996)).Comment: 5 pages, Revte
Quantum-state synthesis of multi-mode bosonic fields: Preparation of arbitrary states of 2-D vibrational motion of trapped ions
We present a universal algorithm for an efficient deterministic preparation
of an arbitrary two--mode bosonic state. In particular, we discuss in detail
preparation of entangled states of a two-dimensional vibrational motion of a
trapped ion via a sequence of laser stimulated Raman transitions. Our formalism
can be generalized for multi-mode bosonic fields. We examine stability of our
algorithm with respect to a technical noise.Comment: 8 pages, revtex, including 2 ps-figures, section about physical
implementation added, references updated, submitted to Phys. Rev. A, computer
program available at http://www.savba.sk/sav/inst/fyzi/qo
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