共查询到20条相似文献,搜索用时 15 毫秒
1.
E. Lundh 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(3):517-520
Two effects are identified that affect the visibility of the
Mott transition in an atomic gas in an optical lattice confined
in a power-law potential. The transition can be made more
pronounced by increasing the power law, but at the same time,
experimental uncertainty in the number of particles will
induce corresponding fluctuations in the measured condensate
fraction. Calculations in two dimensions
indicate that a potential slightly more flat-bottomed than a
quadratic one is to be preferred for a wide range of
particle number fluctuation size. 相似文献
2.
G. Tonini F. Werner Y. Castin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(2):283-294
We investigate theoretically the formation of a vortex lattice in
a superfluid two-spin component Fermi gas in a rotating harmonic trap, in a BCS-type
regime of condensed non-bosonic pairs.
Our analytical solution of the superfluid
hydrodynamic equations, both for the 2D BCS equation of state
and for the 3D unitary quantum gas, predicts that the vortex free gas is
subject to a dynamic instability for fast enough rotation.
With a numerical solution of the full
time dependent BCS equations in a 2D model, we confirm the existence of this dynamic
instability and we show that it leads to the formation of a regular pattern
of quantum vortices in the gas. 相似文献
3.
Y. Castin 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):317-328
We analytically solve two problems that may be useful in the context of the recent observation of matter wave bright solitons
in a one-dimensional attractive atomic Bose gas. The first problem is strictly beyond mean field: from the Bethe ansatz solution
we extract the internal correlation function of the particle positions in the quantum soliton, that is for a fixed center of mass position. The second problem is solved in the limit of a large number of particles, where the mean field theory
is asymptotically correct: it deals with the number of excitations created by the opening of the trap, starting from a pure
soliton in a weakly curved harmonic potential. 相似文献
4.
Sk. Golam Ali B. Talukdar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):315-322
We consider matter-wave bright solitons in the presence of three-body atomic recombination, an axial periodic modulation and
a feeding term, and use a variational method to derive conditions to have dynamically stabilized solitons due to compensation
between the dissipation and alimentation of atoms from external sources. We critically examine how the BEC soliton is affected
by the imbalance between the internal atom loss and external feeding. We pay special attention
to study the influence of these terms on the soliton dynamics in optical lattice potentials that cause periodic modulation. 相似文献
5.
A. B. Bhattacherjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(3):499-506
We study the effect of a one dimensional optical superlattice on the superfluid properties (superfluid fraction, number squeezing,
dynamic structure factor) and the quasi-momentum distribution of the Mott-insulator. We show that due to the secondary lattice,
there is a decrease in the superfluid fraction and the number fluctuation. The dynamic structure factor which can be measured
by Bragg spectroscopy is also suppressed due to the addition of the secondary lattice. The visibility of the interference
pattern (the quasi-momentum distribution) of the Mott-insulator is found to decrease due to the presence of the secondary
lattice. Our results have important implications in atom interferometry and quantum computation in optical lattices. 相似文献
6.
J. Brand A. R. Kolovsky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):331-336
The dynamics of a Bose-Einstein condensate is studied theoretically in a combined periodic plus harmonic external potential.
Different dynamical regimes of stable and unstable collective dipole and Bloch
oscillations are analysed in terms of a quantum mechanical pendulum
model. Nonlinear interactions are shown to counteract quantum-mechanical dephasing and lead to phase-coherent, superfluid
transport. 相似文献
7.
Z. Z. Chen Y. L. Ma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):163-170
The minimal energy configurations of finite Nv-body vortices in a
rotating trapped Bose-Einstein condensate is studied analytically by
extending the previous work [Y. Castin, R. Dum, Eur. Phys. J.
D 7, 399 (1999)], and taking into account the finite
size effects on z-direction and the bending of finite vortex lines. The
calculation of the energy of the vortices as a function of the rotation
frequency of the trap gives number, curvature, configuration of vortices and
width of vortex cores self-consistently. The numerical results show that (1)
the simplest regular polynomial of the several vortex configurations is
energetically favored; while the hexagonal vortex lattice is more stable
than square lattice; (2) bending is more stable then straight vortex line
along the z-axis for λ<1; (3) the boundary effect is obvious:
compared with the estimation made under infinite boundary, the finite size
effect leads to a lower vortex density, while the adding vortex bending
results in a less higher density because of the expansion. The results are
in well agreement with the other authors' ones. 相似文献
8.
Saeed Ghanbari P. Blair Blakie Peter Hannaford Tien D. Kieu 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(3):305-310
The accessibility of the critical parameters for the superfluid to Mott insulator quantum phase transition in a 2D permanent
magnetic lattice is investigated. We determine the hopping
matrix element J, the on-site interaction U, and hence the ratio J/U, in the harmonic oscillator wave function approximation.
We show that for a range of realistic parameters the critical values of J/U, predicted by different methods for the Bose-Hubbard
model in 2D, such as mean field theory and Monte Carlo simulations, are accessible in a 2D permanent magnetic lattice. The
calculations are performed for a 2D permanent magnetic lattice created by two crossed arrays of parallel rectangular magnets
plus a bias magnetic field. 相似文献
9.
M. Rehn S. Bergkvist A. Rosengren R. Saers M. Zelán E. Lundh A. Kastberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(2):223-230
A phase transition for bosonic atoms in a two-dimensional anisotropic optical lattice is considered. If the tunnelling rates
in two directions are different, the system can undergo a transition between a two-dimensional superfluid and a one-dimensional
Mott insulating array of strongly coupled tubes. The connection to other lattice models is exploited in order to better understand
the phase transition. Critical properties are obtained using quantum Monte Carlo calculations. These critical properties are
related to correlation properties of the bosons and a criterion for commensurate filling is established. 相似文献
10.
Josephson oscillation of a superfluid Fermi gas 总被引:1,自引:0,他引:1
S. K. Adhikari 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):413-419
Using the complete numerical solution of a time-dependent
three-dimensional mean-field model we
study the Josephson oscillation of a superfluid Fermi gas (SFG) at zero temperature formed in a combined axially-symmetric
harmonic plus one-dimensional periodic optical-lattice (OL) potentials after displacing the harmonic trap along the axial
OL
axis. We study the dependence of Josephson frequency on the strength of the OL potential. The Josephson frequency decreases
with increasing strength as found in the experiment of Cataliotti et al. [Science 293, 843 (2001)] for a Bose-Einstein condensate and of the experiment of Pezzè et al. [Phys. Rev. Lett. 93, 120401 (2004)] for an ideal Fermi gas. We demonstrate a
breakdown of Josephson oscillation in the SFG for a large displacement
of the harmonic trap. These features of Josephson oscillation of a SFG can be tested experimentally. 相似文献
11.
M.-C. Chung A. R. Kolovsky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):421-425
We consider a Bose-Einstein condensate of ultracold atoms loaded
into a square optical lattice and subject to a static force. For
vanishing atom-atom interactions the atoms perform periodic Bloch
oscillations for arbitrary direction of the force. We study
stability of these oscillations for non-vanishing interactions,
which is shown to depend on an alignment of the force vector with
respect to the lattice crystallographic axes. If the force is
aligned along any of the axes, the mean field approach can be used
to identify the stability conditions. On the contrary, for a
misaligned force one has to employ the microscopic approach, which
predicts periodic modulation of Bloch oscillations in the limit of a
large forcing. 相似文献
12.
H. M. Cataldo D. M. Jezek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(3):585-590
We study the way in which the geometry of the trapping potential affects the vortex velocity in a Bose-Einstein condensate
confined by a toroidal trap. We calculate the vortex precession velocity through a simple relationship between such a velocity
and the gradient of the numerically obtained vortex energy. We observe that our results correspond very closely to the velocity
calculated through time evolution simulations. However, we find that the estimates derived from available velocity field formulas
present appreciable differences. To resolve such discrepancies, we further study the induced velocity field, analyzing the
effect of global features of the condensate on such a field and on the precession velocity. 相似文献
13.
R. Ramakumar A. N. Das 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(2):203-208
We present a theoretical study of bose condensation
of non-interacting bosons in finite lattices in quartic potentials in
one, two, and three dimensions. We investigate dimensionality
effects and quartic potential effects on single boson density of
energy states, condensation temperature, condensate fraction,
and specific heat. The results obtained are compared with
corresponding results for lattice bosons in harmonic traps. 相似文献
14.
R. Ramakumar A. N. Das S. Sil 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):309-316
We present a theoretical study of Bose condensation and specific heat
of non-interacting bosons in finite lattices in harmonic potentials in
one, two, and three dimensions. We numerically diagonalize
the Hamiltonian to obtain the energy levels of the systems.
Using the energy levels thus obtained, we investigate the
temperature dependence, dimensionality effects, lattice size
dependence, and evolution to the bulk limit of the condensate
fraction and the specific heat. Some preliminary results on
the specific heat of fermions in optical lattices are also presented.
The results obtained are contextualized within the current experimental and
theoretical scenario. 相似文献
15.
A. N. Salgueiro A.F.R. de Toledo Piza G. B. Lemos R. Drumond M. C. Nemes M. Weidemüller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):537-540
The dynamics of the population imbalance of bosons in a double-well potential is investigated from the point of view of many-body
quantum mechanics in the framework of the two-mode
model.
For small initial population imbalances, coherent superpositions of almost equally spaced
energy eigenstates lead to Josephson oscillations. The suppression of tunneling at population imbalances beyond a critical
value is related to a high concentration of initial state population in the region of the energy spectrum with quasi-degenerate
doublets. Negligible coherences among adjacent doublets result in imbalance oscillations with a very small amplitude. For
unaccessible long times, however, the system recovers the regime of Josephson oscillations. 相似文献
16.
C. F. Liu Y. Tang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(2):193-199
We provide a mixing model to explore the metastable state
and the macroscopic quantum tunneling (MQT) of binary mixtures. For , we first observe the two condensates form the
symmetry-breaking state (SBS) and then suddenly transfer to the
symmetry-preserving state (SPS) through the MQT. The SBS is shown to be the
metastable state in our system. We find the MQT does not spontaneously
arise. The inducement mechanism is the damping but not the excitations. The
damping mechanism can also control the lifetime and the tunneling decay rate
of the SBS. Finally, we further present the origin of these phenomena by
examining the energy of the system. 相似文献
17.
M. R. Zhang X. Y. Jiang Y. L. Zhang L. Shi J. Zi J. Y. Zhou 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):269-278
We systematically investigate slowly moving matter-wave gap
soliton propagation in weak random optical lattices. With the weak
randomness, an effective-particle theory is constructed to show
that the motion of a gap soliton is similar to a particle moving
in random potentials. Based on the effective-particle theory, the
effects of the randomness on gap solitons are obtained and the
trajectories of gap solitons are well predicted. Moreover, the
general laws that describe the movement depending on the weak
randomness are obtained. We find that with an increase of the
random strength, the ensemble-average velocity reduces slowly and
the reflection probability becomes larger. The theoretical results
based on the effective-particle theory are confirmed by the
numerical simulations based on the Gross-Pitaevskii equation. 相似文献
18.
P. Buonsante S. M. Giampaolo F. Illuminati V. Penna A. Vezzani 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):427-433
We consider strongly interacting boson-boson mixtures on one-dimensional lattices and, by adopting a qualitative mean-field
approach, investigate their quantum phases as the interspecies repulsion is increased. In particular, we analyze the low-energy
quantum emulsion metastable states occurring at large values of the interspecies interaction, which are expected to prevent the system from
reaching its true ground state. We argue a significant decrease in the visibility of the time-of-flight images in the case
of these spontaneously disordered states. 相似文献
19.
D. Jovanović R. Fedele 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):363-368
Two-dimensional stability of a controlled Bose-Einstein
condensation state, in the form of a nonlinear Schr?dinger soliton
[JETP Lett. 80 535 (2004)], is studied
for the condensations with both repulsive and attractive inter-atom
interactions. The Gross-Pitaevski equation is solved numerically,
taking initialy a controlled soliton whose “effective mass” is
several times bigger than the critical value for a weak collapse in
the absence of a potential well, and allowing for reasonably large
errors in the experimental realization of the trapping potential
required by the theory. For repulsive and sufficiently weak
attractive interactions, the controlled state is shown to remain
stable inside a breathing potential well, for a time that is an
order of magnitude longer than the characteristic periods of the
forced and eigenoscillations of the soliton. The collapse is
observed only for attractive interactions, when the nonlinear
attraction exceeded the appropriate threshold.
Electronic supplementary material Supplementary Online Material 相似文献
20.
R. Driben B. A. Malomed 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(3):317-323
It is known that optical-lattice (OL) potentials can stabilize solitons and
solitary vortices against the critical collapse, generated by cubic
attractive nonlinearity in the 2D geometry. We demonstrate that OLs can also
stabilize various species of fundamental and vortical solitons against the
supercritical collapse, driven by the double-attractive cubic-quintic
nonlinearity (however, solitons remain unstable in the case of the pure
quintic nonlinearity). Two types of OLs are considered, producing similar
results: the 2D Kronig-Penney “checkerboard”, and the sinusoidal potential.
Soliton families are obtained by means of a variational approximation, and
as numerical solutions. The stability of all families, which include
fundamental and multi-humped solitons, vortices of oblique and straight
types, vortices built of quadrupoles, and supervortices, strictly
obeys the Vakhitov-Kolokolov criterion. The model applies to optical media
and BEC in “pancake” traps. 相似文献