50 research outputs found
Interacting bosons in two-dimensional lattices with localized dissipation
Motivated by the recent experiment [Takafumi Tomita \emph{et al.}, Sci. Adv.
{\bf 3}, (2017)], we study the dynamics of interacting bosons in a
two-dimensional optical lattice with local dissipation. Together with the
Gutzwiller mean-field theory for density matrices and Lindblad master equation,
we show how the onsite interaction between bosons affects the particle loss for
various strengths of dissipation. For moderate dissipation, the trend in
particle loss differs significantly near the superfluid-Mott boundary than the
deep superfluid regime. While the loss is suppressed for stronger dissipation
in the deep superfluid regime, revealing the typical quantum Zeno effect, the
loss near the phase boundary shows non-monotonic dependence on the dissipation
strength. We furthermore show that close to the phase boundary, the long-time
dynamics is well contrasted with the dissipative dynamics deep into the
superfluid regime. Thus the loss of particle due to dissipation may act as a
probe to differentiate strongly-correlated superfluid regime from its
weakly-correlated counterpart.Comment: 7 pages, 5 figure
Thermal suppression of phase separation in condensate mixtures
We examine the role of thermal fluctuations in binary condensate mixtures of
dilute atomic gases. In particular, we use Hartree-Fock-Bogoliubov with Popov
approximation to probe the impact of non-condensate atoms to the phenomenon of
phase-separation in two-component Bose-Einstein condensates. We demonstrate
that, in comparison to , there is a suppression in the phase-separation of
the binary condensates at . This arises from the interaction of the
condensate atoms with the thermal cloud. We also show that, when it is
possible to distinguish the phase-separated case from miscible from the trends
in the correlation function. However, this is not the case at .Comment: 5 pages, 4 figure
Ramifications of topology and thermal fluctuations in quasi-2D condensates
We explore the topological transformation of quasi-2D Bose-Einstein
condensates of dilute atomic gases, and changes in the low-energy
quasiparticles associated with the geometry of the confining potential. In
particular, we show the density profile of the condensate and quantum
fluctuation follow the transition from a multiply to a simply connected
geometry of the confining potential. The thermal fluctuations, in contrast,
remain multiply connected. The genesis of the key difference lies in the
structure of the low-energy quasiparticles. For which we use the
Hartree-Fock-Bogoliubov, and study the evolution of quasiparticles, the dipole
or the Kohn mode in particular. We, then employ the Hartree-Fock-Bogoliubov
theory with the Popov approximation to investigate the density and the momentum
distribution of the thermal atoms.Comment: 7 pages, 8 figure
Evolution of Goldstone mode in binary condensate mixtures
We show that the third Goldstone mode in the two-species condensate mixtures,
which emerges at phase-separation, gets hardened when the confining potentials
have separated trap centers. The {\em sandwich} type condensate density
profiles, in this case, acquire a {\em side-by-side} density profile
configuration. We use Hartree-Fock-Bogoliubov theory with Popov approximation
to examine the mode evolution and density profiles for these phase transitions
at .Comment: 5 pages, 2 figures. Some part of the theory is common to
arXiv:1307.5716 and arXiv:1405:6459, so that the article is self-contained
for the benefit of the reader
Collective modes in multicomponent condensates with anisotropy
We report the effects of anisotropy in the confining potential on two
component Bose-Einstein condensates (TBECs) through the properties of the low
energy quasiparticle excitations. Starting from generalized Gross Pitaevskii
equation, we obtain the Bogoliubov de-Gennes (BdG) equation for TBECs using the
Hartree-Fock-Bogoliubov (HFB) theory. Based on this theory, we present the
influence of radial anisotropy on TBECs in the immiscible or the
phase-separated domain. In particular, the TBECs of Rb~-Rb and
Cs~-Rb TBECs are chosen as specific examples of the two possible
interface geometries, shell-structured and side by side, in the immiscible
domain. We also show that the dispersion relation for the TBEC shell-structured
interface has two branches, and anisotropy modifies the energy scale and
structure of the two branches.Comment: 9 pages, 13 figure
Bifurcations, stability, and mode evolution in segregated condensate mixtures
We present new features of low energy Bogoliubov quasiparticle excitations of
a two component Bose-Einstein condensate (TBEC) in quasi-2D geometry at zero
temperature using Hartree-Fock-Bogoliubov (HFB). We, in particular, consider
the TBECs of Cs~-Rb and Rb~-Rb, and show specific
features in the low energy excitation spectrum as a function of the interaction
strength. For Rb~-Rb TBEC, the appearance of a new zero energy
mode is observed. Whereas for Cs~-Rb TBEC we report a
bifurcation of the softened Kohn mode at the point of transition from miscible
to immiscible domain. The lower energy mode, after the bifurcation, goes soft
and becomes a new Goldstone mode of the system.Comment: The paper has 9 pages and 12 figure
Design and characterization of a quantum heat pump in a driven quantum gas
We propose the implementation of a quantum heat pump with ultracold atoms. It
is based on two periodically driven coherently coupled quantum dots using
ultracold atoms. Each dot possesses two relevant quantum states and is coupled
to a fermionic reservoir. The working principle is based on energy-selective
driving-induced resonant tunneling processes, where a particle that tunnels
from one dot to the other either absorbs or emits the energy quantum
associated with the driving frequency, depending on its energy.
We characterize the device using Floquet theory and compare simple analytical
estimates to numerical simulations based on the Floquet-Born-Markov formalism.
In particular, we show that driving-induced heating is directly linked to the
micromotion of the Floquet states of the system.Comment: 6 pages, 5 figure
FORTRESS: FORTRAN programs for solving coupled Gross-Pitaevskii equations for spin-orbit coupled spin-1 Bose-Einstein condensate
Here, we present simple and efficient numerical scheme to study static and
dynamic properties of spin-1 Bose-Einstein condensates (BECs) with spin-orbit
(SO) coupling by solving three coupled Gross-Pitaevskii equations (CGPEs) in
three-, quasi-two and quasi-one dimensional systems. We provide a set of three
codes developed in FORTRAN 90/95 programming language with user defined '{\em
option}' of imaginary and real-time propagation. We present the numerical
results for energy, chemical potentials, and component densities for the ground
state and compare with the available results from the literature. The results
are presented for both the ferromagnetic and antiferromagnetic spin-1 BECs with
and without SO coupling. To improve the computational speed, all the codes have
the option of OpenMP parallelization. We have also presented the results for
speedup and efficiency of OpenMP parallelization for the three codes with both
imaginary and real-time propagation