共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Sinatra Y. Castin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):247-260
In the absence of losses the phase of a Bose-Einstein condensate undergoes collapses and revivals in time due to elastic atomic
interactions. As experiments necessarily involve inelastic collisions, we develop a model to describe the phase dynamics of
the condensates in presence of collisional losses. We find that a few inelastic processes are sufficient to damp the revivals of the phase. For this reason the observability of phase revivals for present experimental
conditions is limited to condensates with a few hundreds of atoms.
Received: 23 February 1998 / Revised: 21 July 1998 / Accepted: 23 July 1998 相似文献
2.
Y. Duan H. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):47-51
We find that there exists an elementary topological current in Bose-Einstein condensation. Based on the -mapping topological current theory, the implicit function theorem and the Taylor expansion, the topological structure of
vortex lines is detailed in the neighborhoods of the bifurcation points of the condensate wave function.
Received: 9 April 1998 / Revised: 28 August 1998 / Accepted: 31 August 1998 相似文献
3.
M. Holzmann P. Grüter F. Laloë 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):739-760
We study the occurrence of a Bose-Einstein transition in a dilute gas with repulsive interactions, starting from temperatures
above the transition temperature. The formalism, based on the use of Ursell operators, allows us to evaluate the one-particle
density operator with more flexibility than in mean-field theories, since it does not necessarily coincide with that of an
ideal gas with adjustable parameters (chemical potential, etc.). In a first step, a simple approximation is used (Ursell-Dyson
approximation), which allow us to recover results which are similar to those of the usual mean-field theories. In a second
step, a more precise treatment of the correlations and velocity dependence of the populations in the system is elaborated.
This introduces new physical effects, such as a change of the velocity profile just above the transition: the proportion of
atoms with low velocities is higher than in an ideal gas. A consequence of this distortion is an increase of the critical
temperature (at constant density) of the Bose gas, in agreement with those of recent path integral Monte-Carlo calculations
for hard spheres.
Received 13 November 1998 相似文献
4.
M. Modugno L. Pricoupenko Y. Castin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(2):235-257
We consider a 3D dilute Bose-Einstein condensate at thermal equilibrium in a rotating harmonic trap. The condensate wavefunction
is a local minimum of the Gross-Pitaevskii energy functional and we determine it numerically with the very efficient conjugate
gradient method. For single vortex configurations in a cigar-shaped harmonic trap we find that the vortex line is bent, in
agreement with the numerical prediction of Garcia-Ripoll and Perez-Garcia [Phys. Rev. A 63, 041603 (2001)]. We derive a simple energy functional for the vortex line in a cigar-shaped condensate which allows to understand
physically why the vortex line bends and to predict analytically the minimal rotation frequency required to stabilize the
bent vortex line. This analytical prediction is in excellent agreement with the numerical results. It also allows to find
in a simple way a saddle point of the energy, where the vortex line is in a stationary configuration in the rotating frame
but not a local minimum of energy. Finally we investigate numerically the effect of thermal fluctuations on the vortex line
for a condensate with a straight vortex: we can predict what happens in a single realization of the experiment by a Monte
Carlo sampling of an atomic field quasi-distribution function of the density operator of the gas at thermal equilibrium in
the Bogoliubov approximation.
Received 28 March 2002 / Received in final form 13 September 2002 Published online 21 January 2003
RID="a"
ID="a"e-mail: yvan.castin@lkb.ens.fr 相似文献
5.
J. Ruostekoski D.F. Walls 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(3):335-339
Two Bose-Einstein condensates in different Zeeman sublevels can be decoupled from driving light fields in coherent population
trapping. A condensate pair with a deterministic entanglement and a controllable value of the relative phase may be prepared
by selecting the phase difference between the coherent light fields. The rate of the condensate phase diffusion may be determined
from the two-photon resonant absorption of radiation.
Received: 29 June 1998 / Revised: 10 October 1998 / Accepted: 19 October 1998 相似文献
6.
A. Sinatra Y. Castin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(3):319-332
We investigate the relative phase coherence properties and the occurrence of demixing instabilities for two mutually interacting
and time evolving Bose-Einstein condensates in traps. Our treatment naturally includes the additional decoherence effect due
to fluctuations in the total number of particles. Analytical results are presented for the breathe-together solution, an extension
of previously known scaling solution to the case of a binary mixture of condensates. When the three coupling constants describing
the elastic interactions among the atoms in the two states are close to each other, a dramatic increase of the phase coherence
time is predicted. Numerical results are presented for the parameters of the recent JILA experiments.
Received 23 April 1999 and Received in final form 21 September 1999 相似文献
7.
Y. Castin R. Dum 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):399-412
We investigate minimal energy solutions with vortices for an interacting Bose-Einstein condensate in a rotating trap. The
atoms are strongly confined along the axis of rotation z, leading to an effective 2D situation in the x-y plane. We first use a simple numerical algorithm converging to local minima of energy. Inspired by the numerical results
we present a variational ansatz in the regime where the interaction energy per particle is stronger than the quantum of vibration
in the harmonic trap in the x-y plane, the so-called Thomas-Fermi regime. This ansatz allows an easy calculation of the energy of the vortices as function
of the rotation frequency of the trap; it gives a physical understanding of the stabilisation of vortices by rotation of the
trap and of the spatial arrangement of vortex cores. We also present analytical results concerning the possibility of detecting
vortices by a time-of-flight measurement or by interference effects. In the final section we give numerical results for a
3D configuration.
Received 16 December 1998 and Received in final form 18 March 1999 相似文献
8.
9.
C. Lichtenberg G. Marx G. Tommaseo P.N. Ghosh G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):29-32
On the basis of a macroscopic ground state population it was argued recently that Bose-Einstein condensation should occur
in a one-dimensional harmonic potential. We examine this situation by drawing analogies to bosons in a two-dimensional box,
where the thermodynamic limit is well-defined. We show that in both systems although the ground state populations show sharp
onsets at the critical temperature, the behaviour of the specific heat is analytic, which proves the absence of a phase transition
in these systems.
Received: 17 February 1997 / Revised: 3 September 1997 / Accepted: 13 October 1997 相似文献
10.
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
11.
E. Braaten A. Nieto 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):143-159
Quantum corrections to the properties of a homogeneous interacting Bose gas at zero temperature can be calculated as a low-density
expansion in powers of , where is the number density and a is the S-wave scattering length. We calculate the ground state energy density to second order in . The coefficient of the correction has a logarithmic term that was calculated in 1959. We present the first calculation of the constant under the
logarithm. The constant depends not only on a, but also on an extra parameter that describes the low energy scattering of the bosons. In the case of alkali atoms, we argue that the second order quantum correction is dominated by
the logarithmic term, where the argument of the logarithm is ,and is the length scale set by the van der Waals potential.
Received 2 February 1999 相似文献
12.
A. Montina E. Arimondo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):105-110
In this article we introduce a differential equation for the first order correlation function G
(1) of a Bose-Einstein condensate at T = 0. The Bogoliubov approximation is used. Our approach points out directly the dependence on the physical parameters. Furthermore
it suggests a numerical method to calculate G
(1) without solving an eigenvector problem. The G
(1) equation is generalized to the case of non zero temperature.
Received 20 September 2000 相似文献
13.
A. Smerzi A. Trombettoni T. Lopez-Arias C. Fort P. Maddaloni F. Minardi M. Inguscio 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):457-461
We demonstrate, both from a theoretical and an experimental point of view, the possibility of realizing a weak coupling between
two Bose-Einstein condensates trapped in different Zeeman states. The weak coupling drives macroscopic quantum oscillations
between the condensate populations and the observed current-phase dynamics is described by generalized Josephson equations.
In order to highlight the superfluid nature of the oscillations, we investigate the response of a 87Rb non-condensate (thermal) gas in the same conditions, showing that the thermal oscillations damp more quickly than those
of the condensate.
Received 2 May 2002 / Received in final form 19 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: smerzi@sissa.it 相似文献
14.
K.-P. Marzlin W. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(2):241-253
An extended Bose-Einstein condensate (BEC) in an optical lattice provides a kind of periodic dielectric and causes band gaps
to occur in the spectrum of light propagating through it. We examine the question whether these band gaps can modify the spontaneous
emission rate of atoms excited from the BEC, and whether they can lead to a self-stabilization of the BEC against spontaneous
emission. We find that self-stabilization is not possible for BECs with a density in the order of 1014 cm-3. However, the corresponding non-Markovian behavior produces significant effects in the decay of excited atoms even for a
homogeneous BEC interacting with a weak laser beam. These effects are caused by the occurrence of an avoided crossing in the
photon (or rather polariton) spectrum. We also predict a new channel for spontaneous decay which arises from an interference
between periodically excited atoms and periodic photon modes. This new channel should also occur in ordinary periodic dielectrics.
Received 27 March 2000 相似文献
15.
Z.-Ch. Wang H.-W. Yang S. Yin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):117-119
Starting from the Gross-Pitaevskii energy functional of the 3D Bose-Einstein Condensate, we derive approximately the energy
functional and the effective coupling constant of the quasi-2D condensate. The evolution of the quasi-2D condensate wave function
is studied by a variational method. Low energy excitation spectra for both positive and negative scattering lengths are analyzed.
The condition of collapse instability of a quasi-2D Bose gas with attractive particle interaction is also proposed.
Received 31 October 2001 / Received in final form 1st March 2002 Published online 28 June 2002 相似文献
16.
J. Schneider H. Wallis 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):507-512
The superfluid fraction of an atomic cloud is defined using the cloud's response to a rotation of the external potential,
i.e. the moment of inertia. A fully quantum mechanical calculation of this moment is based on the dispersion of Lz instead of quasi-classical averages. In this paper we derive analytical results for the moment of inertia of a small number
of non-interacting Bosons using the canonical ensemble. The required symmetrized averages are obtained via a representation of the partition function by permutation cycles. Our results are useful to discriminate purely quantum statistical
effects from interaction effects in studies of superfluidity and phase transitions in finite samples.
Received 30 June 2000 相似文献
17.
G. Baym J.-P. Blaizot M. Holzmann F. Laloë D. Vautherin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):107-124
We study the effects of repulsive interactions on the critical density for the Bose-Einstein transition in a homogeneous dilute
gas of bosons. First, we point out that the simple mean field approximation produces no change in the critical density, or
critical temperature, and discuss the inadequacies of various contradictory results in the literature. Then, both within the
frameworks of Ursell operators and of Green's functions, we derive self-consistent equations that include correlations in
the system and predict the change of the critical density. We argue that the dominant contribution to this change can be obtained
within classical field theory and show that the lowest order correction introduced by interactions is linear in the scattering
length, a, with a positive coefficient. Finally, we calculate this coefficient within various approximations, and compare with various
recent numerical estimates.
Received 15 July 2001 相似文献
18.
L. Vichi M. Amoruso A. Minguzzi S. Stringari M.P. Tosi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):335-339
We study a confined mixture of bosons and fermions in the regime of quantal degeneracy, with particular attention to the effects
of the interactions on the kinetic energy of the fermionic component. We are able to explore a wide region of system parameters
by identifying two scaling variables which completely determine its state at low temperature. These are the ratio of the boson-fermion
and boson-boson interaction strengths and the ratio of the radii of the two clouds. We find that the effect of the interactions
can be sizeable for reasonable choices of the parameters and that its experimental study can be used to infer the sign of
the boson-fermion scattering length. The interplay between interactions and thermal effects in the fermionic kinetic energy
is also discussed.
Received 13 September 1999 and Received in final form 22 February 2000 相似文献
19.
J.O. Andersen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):389-396
We consider an interacting homogeneous Bose gas at zero temperature in two spatial dimensions. The properties of the system
can be calculated as an expansion in powers of g, where g is the coupling constant. We calculate the ground state pressure and the ground state energy density to second order in the
quantum loop expansion. The renormalization group is used to sum up leading and subleading logarithms from all orders in perturbation
theory. In the dilute limit, the renormalization group improved pressure and energy density are expansions in powers of the
T
2B and T
2Bln(T
2B), respectively, where T
2B is the two-body T-matrix.
Received 19 April 2002 Published online 13 August 2002 相似文献
20.
M.P. Singh A.L. Satheesha 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):391-398
We propose a simple variational form of the wave function to describe the ground state and vortex states of a weakly interacting
Bose gas in an anisotropic trap. The proposed wave function is valid for a wide range of the particle numbers in the trap.
It also works well in the case of attractive interaction between the atoms. Further, it provides an easy and fast method to
calculate the physical quantities of interest. The results compare very well with those obtained by purely numerical techniques.
Using our wave function we have been able to verify, for the first time, the predicted behaviour of the aspect ratio.
Received 7 December 1998 and Received in final form 4 February 1999 相似文献