共查询到20条相似文献,搜索用时 15 毫秒
1.
D. Guerra R. Méndez-Galain N. Wschebor 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):357-365
The usual procedure of including a finite number of vertices in Non Perturbative Renormalization Group equations in order
to obtain n-point correlation functions at finite momenta is analyzed.
This is done by exploiting a general method recently introduced which includes simultaneously all vertices
although approximating their momentum dependence. The study is performed using the self-energy of the tridimensional scalar
model at criticality.
At least in this example, low order truncations miss quantities as the critical exponent η by as much as 60%. However, if
one goes to high order truncations the procedure seems to converge rapidly. 相似文献
2.
A. E. Bernardini 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):151-155
The quartic confining potential has emerged as a key ingredient to obtain
fast rotating vortices in BEC as well as observation of quantum phase
transitions in optical lattices. We calculate the critical temperature
Tc of bosons at which normal to BEC transition occurs for the quartic
confining potential. Further more, we evaluate the effect of finite
particle number on Tc and find that ΔTc/Tc is
larger in quartic potential as compared to quadratic potential for number
of particles <105. Interestingly, the situation is reversed if
the number of particles is
105. 相似文献
3.
Y. Hao Y. Zhang J. Q. Liang S. Chen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):541-545
We investigate the effect of the anisotropic spin-spin interaction
on the ground state density distribution of the one dimensional
spin-1 bosonic gases within a modified Gross-Pitaevskii theory
both in the weakly interaction regime and in the Tonks-Girardeau
(TG) regime. We find that for ferromagnetic spinor gas the phase
separation occurs even for weak anisotropy of the spin-spin
interaction, which becomes more and more obvious and the component
of mF=0 diminishes as the anisotropy increases. However, no
phase separation is found for anti-ferromagnetic spinor gas in
both regimes. 相似文献
4.
Y.-M. Kao T. F. Jiang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):263-269
The thermodynamic properties of the trapped ideal spinor Bose gas are
studied in details with the constraints of fixed total number of atoms N, and
magnetization M. The double transition temperatures, their
corresponding corrections due to finite particle number, and the
population of each component are investigated. The generalization
to the ideal spinor Bose gas of hyperfine quantum number F is
also discussed. We propose that the order and disorder parameters
to describe the symmetry broken of condensation. 相似文献
5.
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
6.
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
7.
T. Gottwald P. G.J. van Dongen 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):277-285
In order to describe unbalanced ultracold fermionic quantum gases on optical lattices in a harmonic trap, we investigate an
attractive (U < 0) asymmetric (t↑≠t↓) Hubbard model with a Zeeman-like magnetic field. In view of the model's spatial inhomogeneity, we focus in this paper on
the solution at Hartree-Fock level. The Hartree-Fock Hamiltonian is diagonalized with particular emphasis on superfluid phases.
For the special case of spin-independent hopping we analytically determine the number of solutions of the resulting self-consistency
equations and the nature of the possible ground states at weak coupling. We present the phase diagram of the homogeneous system
and numerical results for unbalanced Fermi-mixtures obtained within the local density approximation. In particular, we find
a fascinating shell structure, involving normal and superfluid phases. For the general case of spin-dependent hopping we calculate
the density of states and the possible superfluid phases in the ground state. In particular, we find a new magnetized superfluid
phase. 相似文献
8.
M. Takahashi S. Ghosh T. Mizushima K. Machida 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):391-400
We show that the effective theory of long wavelength low energy behavior of a dipolar Bose-Einstein condensate(BEC) with large
dipole moments (treated as a classical spin) can be modeled using an extended non-linear sigma model (NLSM) like energy functional
with an additional non-local term that represents long ranged anisotropic dipole-dipole interaction. Minimizing this effective
energy functional we calculate the density and spin-profile of the dipolar Bose-Einstein condensate in the mean-field regime
for various trapping geometries. The resulting configurations show strong intertwining between the spin and mass density of
the condensate, transfer between spin and orbital angular momentum in the form of Einstein-de Hass effect, and novel topological
properties. We have also described the theoretical framework in which the collective excitations around these mean field solutions
can be studied and discuss some examples qualitatively. 相似文献
9.
K. P. Schmidt A. Reischl G. S. Uhrig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):343-352
In this work we give a consistent picture of the thermodynamic properties of
bosons in the Mott insulating phase when loaded adiabatically into
one-dimensional optical lattices. We find a crucial dependence of the
temperature in the optical lattice on the doping level of the Mott
insulator. In the undoped case, the temperature is of the order of the large
onsite
Hubbard interaction. In contrast, at a finite doping level the
temperature jumps almost immediately to the order of the small hopping
parameter. These two situations are investigated on the one hand by considering
limiting cases like the atomic limit and the case of free fermions. On the
other hand, they are examined using a quasi-particle conserving continuous
unitary transformation extended by an approximate thermodynamics for
hardcore particles. 相似文献
10.
Y. J. Hao S. Chen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(2):261-266
We study ground-state properties of interacting two-component boson gases in a one-dimensional harmonic trap by using the
exact numerical diagonalization method. Based on numerical solutions of many-body Hamiltonians, we calculate the ground-state
density distributions in the whole interaction regime for different atomic number ratio, intra- and inter-atomic interactions.
For the case with equal intra- and inter-atomic interactions, our results clearly display the evolution of density distributions
from a Bose condensate distribution to a Fermi-like distribution with the increase of the repulsive interaction. Particularly,
we compare our result in the strong interaction regime to the exact result in the infinitely repulsive limit which can be
obtained by a generalized Bose-Fermi mapping. We also discuss the general case with different intra- and inter-atomic interactions
and show the rich configurations of the density profiles. 相似文献
11.
Bosonic properties of α particles such as single-α orbits and occupation numbers in Jπ = 0+, 2+, 1- and 3- states of 12C around the 3α threshold are investigated with the semi-microscopic 3α cluster model. As in other studies, we found that
the 0+2 (2+2) state has dilute-3α-condensate-like structure in which the α particle is occupied in the single S (D) orbit with about 70% (80%) probability. The radial behaviors of the single-α orbits as well as the occupation numbers are
discussed in detail in comparison with those for the 0+1 and 2+1 states together with the 1-1 and 3-1 states. 相似文献
12.
We explore the many body physics of a Bose condensed atom gas at finite temperature through the Raman transition between two
hyperfine levels. Unlike the Bragg scattering where the phonon-like nature of the collective excitations has been observed,
a different branch of thermal atom excitation is found theoretically in the Raman scattering. This excitation is predicted
in the generalized random phase approximation (GRPA) and has a gapped and parabolic dispersion relation. The gap energy results
from the exchange interaction and is released during the Raman transition. The scattering rate is determined versus the transition
frequency ω and the transferred momentum q and shows the corresponding resonance around this gap. Nevertheless, the Raman
scattering process is attenuated by the superfluid part of the gas. The macroscopic wave function of the condensate deforms
its shape in order to screen locally the external potential displayed by the Raman light beams. This screening is total for
a condensed atom transition in order to prevent the condensate from incoherent scattering. The experimental observation of
this result would explain some of the reasons why asuperfluid condensate moves coherentlywithout any friction with its surrounding. 相似文献
13.
Shyamal Biswas 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(1):109-112
We study the Bose-Einstein condensation for a 3-d system of ideal Bose gas which is harmonically trapped along two perpendicular
directions and is confined in between two slabs along the other perpendicular direction. We calculate the Casimir force between
the two slabs for this system of trapped Bose gas. At finite temperatures this force for thermalized photons in between two
plates has a classical expression which is independent of ħ. At finite temperatures the Casimir force for our system depends
on ħ. For the calculation of Casimir force we consider only the Dirichlet boundary condition. We show that below condensation
temperature (Tc) the Casimir force for this non-interacting system decreases with temperature (T) and at
, it is independent of temperature. We also discuss the Casimir effect on 3-d highly anisotropic harmonically trapped ideal
Bose gas. 相似文献
14.
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
15.
N. Bera J. K. Bhattacharjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(1):21-26
An exact calculation of the Casimir force for a non-interacting Bose gas confined between two parallel plates is presented. The gas can be free or trapped, parallel to the plates. Depending on the finite size parameter λ/L (λ is the de Bröglie wavelength and L is the separation of the plates) and the density parameter nλ3 (n, the number density), the Casimir force crosses over from a power law to an exponential fall off is clearly seen. Since the Casimir force measurement requires very small values of L, one needs to take into account of the condensation in a finite system. 相似文献
16.
E. P. Zemskov K. Kassner M. A. Tsyganov M. J.B. Hauser 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,72(3):457-465
Using a field-theoretic approach, we systematically generalize the usual semiclassical approximation for a harmonically trapped
ideal Bose gas in such a way that its range of applicability is essentially extended. With this we can analytically calculate
thermodynamic properties even for small particle numbers. In particular, it now becomes possible to determine the critical
temperature as well as the temperature dependence of both heat capacity and condensate fraction in low-dimensional traps,
where the standard semiclassical approximation is not even applicable. 相似文献
17.
R. Hoppeler J. Viana Gomes D. Boiron 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):157-162
We have studied the atomic density of a cloud confined
in an isotropic harmonic trap at the vicinity of the Bose-Einstein
transition temperature. We show that, for a non-interacting gas
and near this temperature, the ground-state density has the same
order of magnitude as the excited states density at the centre of
the trap. This holds in a range of temperatures where the
ground-state population is negligible compared to the total atom
number. We compare the exact calculations, available in a harmonic
trap, to semi-classical approximations. We show that these latter
should include the ground-state contribution to be accurate. 相似文献
18.
S. K. Adhikari 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):279-286
Using variational and numerical solutions we show that
stationary
negative-energy localized (normalizable) bound states can appear in the
three-dimensional nonlinear Schr?dinger equation with a finite
square-well potential for a range of nonlinearity parameters. Below a
critical attractive nonlinearity, the system becomes unstable and
experiences collapse. Above a limiting repulsive nonlinearity, the
system becomes highly repulsive and cannot be bound. The system also
allows nonnormalizable states of infinite norm at positive energies in
the continuum. The normalizable negative-energy bound states could be
created in BECs and studied in the laboratory with present knowhow. 相似文献
19.
M. Amoruso A. Minguzzi S. Stringari M.P. Tosi L. Vichi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):261-265
We present a semiclassical three-fluid model for a Bose-condensed mixture of interacting Bose and Fermi gases confined in
harmonic traps at finite temperature. The model is used to characterize the experimentally relevant behaviour of the equilibrium
density profile of the fermions with varying composition and temperature across the onset of degeneracy, for coupling strengths
relevant to a mixture of 39K and 40K atoms.
Received: 18 May 1998 / Revised: 24 August 1998 / Accepted: 31 August 1998 相似文献
20.
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