912 research outputs found
Splitting between quadrupole modes of dilute quantum gas in a two dimensional anisotropic trap
We consider quadrupole excitations of quasi-two dimensional interacting
quantum gas in an anisotropic harmonic oscillator potential at zero
temperature. Using the time-dependent variational approach, we calculate a few
low-lying collective excitation frequencies of a two dimensional anisotropic
Bose gas. Within the energy weighted sum-rule approach, we derive a general
dispersion relation of two quadrupole excitations of a two dimensional deformed
trapped quantum gas. This dispersion relation is valid for both statistics. We
show that the quadrupole excitation frequencies obtained from both methods are
exactly the same. Using this general dispersion relation, we also calculate the
quadrupole frequencies of a two dimensional unpolarized Fermi gas in an
anisotropic trap. For both cases, we obtain analytic expressions for the
quadrupole frequencies and the splitting between them for arbitrary value of
trap deformation. This splitting decreases with increasing interaction strength
for both statistics. For two dimensional anisotropic Fermi gas, the two
quadrupole frequencies and the splitting between them become independent of the
particle number within the Thomas-Fermi approach.Comment: 8 pages, 3 ps figs, to appear in The European Physical Journal
Trapped two-dimensional condensates with synthetic spin-orbit coupling
We study trapped 2D atomic Bose-Einstein condensates with spin-independent
interactions in the presence of an isotropic spin-orbit coupling, showing that
a rich physics results from the non-trivial interplay between spin-orbit
coupling, confinement and inter-atomic interactions. For low interactions two
types of half-vortex solutions with different winding occur, whereas
strong-enough repulsive interactions result in a stripe-phase similar to that
predicted for homogeneous condensates. Intermediate interaction regimes are
characterized for large enough spin-orbit coupling by an hexagonally-symmetric
phase with a triangular lattice of density minima similar to that observed in
rapidly rotating condensates.Comment: 4 pages, 3 figures,reduced the resolution of figure 1 from previous
submissio
Emergence of a quasi-ergodic steady state in a dissipative Tavis-Cummings array
In an atom-photon interacting system described by Tavis Cummings Hubbard
(TCH) model, we demonstrate the emergence of a quasi-steady state in a
dissipative environment that exhibits intriguing ergodic behavior. The TCH
model undergoes a dissipative transition from normal to superradiant phase
hosting a gapped Higgs and gapless Goldstone modes. However, in a large region
of the phase diagram, the instability of the Goldstone mode leads to the
disappearance of the stable superradiant phase. In this regime, the
decorrelator dynamics reveals light cone spreading of the perturbations and
positive Lyapunov exponent, indicating enhanced fluctuations. Remarkably, a
quasi-steady state emerges under quench dynamics in this unstable regime; in
this state, a class of collective quantities such as site averaged photon
number and atomic excitations approach a steady value, in spite of large
temporal fluctuations in corresponding microscopic variables. This quasi-steady
state describes an incoherent fluid of photons with significant phase
fluctuation. The phase space dynamics reveals a fascinating ergodic behavior in
presence of dissipation, leading to the characterization of the dynamical
variables into two distinct classes. The first class includes site-averaged
photon numbers and atomic excitations; these exhibit a stationary distribution
regardless of the initial condition indicating ergodic behavior. The second
class of variables, particularly those related to phase in contrast, retain
information about the initial conditions, resulting in a violation of
ergodicity for finite size system. Additionally, the dynamical variables of the
ergodic class exhibit fascinating collective scarring phenomenon as the peak of
their distribution is attracted towards the unstable steady state, analogous to
the single particle quantum scar. We discuss the relevance of our findings in
the current experiments
Friction and diffusion of matter-wave bright solitons
We consider the motion of a matter-wave bright soliton under the influence of
a cloud of thermal particles. In the ideal one-dimensional system, the
scattering process of the quasiparticles with the soliton is reflectionless,
however, the quasiparticles acquire a phase shift. In the realistic system of a
Bose-Einstein condensate confined in a tight waveguide trap, the transverse
degrees of freedom generate an extra but small nonlinearity in the system which
gives rise to finite reflection and leads to dissipative motion of the soliton.
We calculate the velocity and temperature-dependent frictional force and
diffusion coefficient of a matter wave bright soliton immersed in a thermal
cloud
A new non-perturbative approach to Quantum Brownian Motion
Starting from the Caldeira-Leggett (CL) model, we derive the equation
describing the Quantum Brownian motion, which has been originally proposed by
Dekker purely from phenomenological basis containing extra anomalous diffusion
terms. Explicit analytical expressions for the temperature dependence of the
diffusion constants are derived. At high temperatures, additional momentum
diffusion terms are suppressed and classical Langivin equation can be recovered
and at the same time positivity of the density matrix(DM) is satisfied. At low
temperatures, the diffusion constants have a finite positive value, however,
below a certain critical temperature, the Master Equation(ME) does not satisfy
the positivity condition as proposed by Dekker.Comment: 5 page
Rotating fermions in two dimensions: Thomas Fermi approach
Properties of confined mesoscopic systems have been extensively studied
numerically over recent years. We discuss an analytical approach to the study
of finite rotating fermionic systems in two dimension. We first construct the
energy functional for a finite fermionic system within the Thomas-Fermi
approximation in two dimensions. We show that for specific interactions the
problem may be exactly solved. We derive analytical expressions for the
density, the critical size as well as the ground state energy of such systems
in a given angular momentum sector.Comment: Latex 15 pages, 3 ps. figures. Poster in SCES-Y2K, held at SAHA
Institute of Nuclear Physics,Calcutta,October (2000
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