202 research outputs found
Effect of Weak Disorder on the BCS-BEC crossover in a two-dimensional Fermi Gas
In this article we study the two-dimensional (2D) ultracold Fermi gas with
weak impurity in the framework of mean-field theory where the impurity is
introduced through Gaussian fluctuations. We have investigated the role of the
impurity by studying the experimentally accessible quantities such as
condensate fraction and equation of state of the ultracold systems. Our
analysis reveals that, at the crossover the disorder enhances superfluidity,
which we attribute to the unique nature of the unitary region and to the
dimensional effect.Comment: To appear in Int. J. Mod. Phys.
Investigating Dirty Crossover through Fidelity Susceptibility and Density of States
We investigate the BCS-BEC crossover in an ultracold atomic gas in the
presence of disorder. The disorder is incorporated in the mean-field formalism
through Gaussian fluctuations. We observe evolution to an asymmetric line-shape
of fidelity susceptibility as a function of interaction coupling with
increasing disorder strength which may point to an impending quantum phase
transition. The asymmetric line-shape is further analyzed using the statistical
tools of skewness and kurtosis. We extend our analysis to density of states
(DOS) for a better understanding of the crossover in the disordered
environment.Comment: 12 pages, 6 figures. To appear in Int. J. Mod. Phys.
Topology of Quantum Grey Soliton in Multi-Component Inhomogeneous Bose-Einstein Condensates
We study the dispersion mechanism of Lieb mode excitations of both single and
multi component ultra-cold atomic Bose gas, subject to a harmonic confinement
through chirp management. It is shown that in some parameter domain, the
hole-like excitations lead to the soliton's negative mass regime, arising due
to the coupling between chirp momentum and Kohn mode. In low momenta region the
trap considerably affects the dispersion of the grey soliton, which opens a new
window to observe Lieb-mode excitations. Further, we extend our analysis to
binary condensate, which yields usual shape compatible grey-bright soliton
pairs. The inter-species interaction induces a shift in the Lieb-mode
excitations, where the pair can form a bound state. We emphasize that the
present model provides an opportunity to study such excitations in the low
momenta regime, as well as the formation of bound state in binary condensate.Comment: 9 pages, 7 figure
Effect of Disorder in BCS-BEC Crossover
In this article we have investigated the effect of weak random disorder in
the BCS-BEC crossover region. The disorder is included in the mean field
formalism through NSR theory of superconducting fluctuations. A self consistent
numerical solution of the coupled equations involving the superfluid gap
parameter and density as a function of the disorder strength, albeit unaffected
in the BCS phase, yields a depleted order parameter in the BEC regime and an
interesting nonmonotonic behavior of the condensate fraction in the vicinity of
the unitary region, and a gradual depletion thereafter, as the pairing
interaction is continuously tuned across the BCS-BEC crossover. The unitary
regime thus demonstrates a robust paradigm of superfluidity even when the
disorder is introduced. To support the above feature and shed light on a
lingering controversial issue, we have computed the behavior of the sound mode
across the crossover that distinctly reveals a suppression of the sound
velocity. We also find the Landau critical velocity that shows similar
nonmonotonicity as that of the condensate fraction data, thereby supporting a
stable superfluid scenario in the unitary limit
On Solving Cubic-Quartic Nonlinear Schr\"odinger Equation in a Cnoidal Trap
The recent observations of quantum droplet in ultra-cold atomic gases have
opened up new avenues of fundamental research. The competition between
mean-field and beyond mean-field interactions, in ultra-cold dilute alkali
gases, are believed to be instrumental in stabilizing the droplets. These new
understanding has motivated us to investigate the analytical solutions of a
trapped cubic-quartic nonlinear Schr\"odinger equation (CQNLSE). The quartic
contribution in the NLSE is derived from the beyond mean-field formalism of
Bose-Einstein condensate (BEC). To the best of our knowledge, a comprehensive
analytical description of CQNLSE is non-existent. Here, we study the existence
of the analytical solutions which are of the cnoidal type for CQNLSE. The
external trapping plays a significant role in the stabilization of the system.
In the limiting case, the cnoidal wave solutions lead to the localized solution
of bright solution and delocalized kink-antikink pair. The nonexistence of the
sinusoidal mode in the current scheme is also revealed in our analysis.Comment: Extensively modified from v1. To appear in Eur. Phys. J.
Tunneling dynamics of correlated bosons in a double well potential
The quantum dynamics of a few bosons in a double well potential is studied
using a Bose Hubbard model. We consider both signs for the on-site
interparticle interaction and also investigated the situations where they are
large and small. Interesting distinctive features are noted for the tunneling
oscillations of these bosons corresponding to the above scenarios. Further, the
sensitivity of the particle dynamics to the initial conditions has been
studied. It is found that corresponding to an odd number of particles, such as
three (or five), an initial condition of having unequal number of particles in
the wells has interesting consequences, which is most discernible when the
population difference between the wells is unity.Comment: To appear in Eur. Phys. J.
Bell Soliton in Ultra-cold Atomic Fermi Gas
We demonstrate the existence of supersonic bell soliton in the
Bardeen-Cooper-Schrieffer-Bose-Einstein condensate (BCS-BEC) crossover regime.
Starting from the extended Thomas-Fermi density functional theory of superfluid
order parameter, a density transformation is used to map the hydrodynamic mean
field equation to a Lienard type equation. As a result, bell solitons are
obtained as exact solutions, which is further verified by the numerical
solution of the dynamical equation. The stability of the soliton is established
and its behaviour in the entire crossover domain is obtained. It is found that,
akin to the case of vortices, the bell solitons yield highest contrast in the
BEC regime.Comment: Please consider Eq.(2) of the current version as correct one instead
of Eq.(2) in the previous version and Journal versio
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