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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.
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
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.
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
5.
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
6.
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
7.
8.
T.K. Ghosh S. Sinha 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):371-378
We consider quadrupole excitations of quasi-two-dimensional interacting quantum gas in an anisotropic harmonic oscillator
potential at zero temperature. Using the time-dependent variational approach, we calculate a few low-lying collective excitation
frequencies of a two-dimensional anisotropic Bose gas. Within the energy weighted sum-rule approach, we derive a general dispersion
relation of two quadrupole excitations of a two-dimensional deformed trapped quantum gas. This dispersion relation is valid
for both statistics. We show that the quadrupole excitation frequencies obtained from both methods are exactly the same. Using
this general dispersion relation, we also calculate the quadrupole frequencies of a two-dimensional unpolarized Fermi gas
in an anisotropic trap. For both cases, we obtain analytic expressions for the quadrupole frequencies and the splitting between
them for arbitrary value of trap deformation. This splitting decreases with increasing interaction strength for both statistics.
For a two-dimensional anisotropic Fermi gas, the two quadrupole frequencies and the splitting between them become independent
of the particle number within the Thomas-Fermi approach.
Received 21 September 2001 and Received in final form 9 December 2001 相似文献
9.
Z.P. Karkuszewski K. Sacha A. Smerzi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):251-254
We study a Bose-Einstein condensate trapped in an asymmetric double well potential. Solutions of the time-independent Gross-Pitaevskii
equation reveal intrinsic loops in the energy (or chemical potential) level behavior when the shape of the potential is varied.
We investigate the corresponding behavior of the quantum (many-body) energy levels. Applying the two-mode approximation to
the bosonic field operators, we show that the quantum energy levels create an anti-crossing net inside the region bounded
by the loop of the mean field solution.
Received 6 March 2002 / Received in final form 19 September 2002 Published online 15 November 2002
RID="a"
ID="a"e-mail: smerzi@cnls.lanl.gov 相似文献
10.
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
11.
E. Mandonnet A. Minguzzi R. Dum I. Carusotto Y. Castin J. Dalibard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):9-18
We present a theoretical analysis of the evaporative cooling of an atomic beam propagating in a magnetic guide. Cooling is
provided by transverse evaporation. The atomic dynamics inside the guide is analyzed by solving the Boltzmann equation with
two different approaches: an approximate analytical ansatz and a Monte-Carlo simulation. Within their domain of validity,
these two methods are found to be in very good agreement with each other. They allow us to determine how the phase-space density
and the flux of the beam vary along its direction of propagation. We find a significant increase for the phase-space density
along the guide for realistic experimental parameters. By extrapolation, we estimate the length of the beam needed to reach
quantum degeneracy.
Received 24 September 1999 相似文献
12.
B. Pozzi L. Salasnich A. Parola L. Reatto 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):367-370
We study the thermodynamics of the Bose-condensed atomic hydrogen confined in the Ioffe-Pritchard potential. Such a trapping
potential, that models the magnetic trap used in recent experiments with hydrogen, is anharmonic and strongly anisotropic.
We calculate the ground-state properties, the condensed and non-condensed fraction and the Bose-Einstein transition temperature.
The thermodynamics of the system is strongly affected by the anharmonicity of this external trap. Finally, we consider the
possibility to detect Josephson-like currents by creating a double-well barrier with a laser beam.
Received 15 February 2000 相似文献
13.
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
14.
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
15.
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
16.
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
17.
Y.-B. Zhang H.J.W. Müller-Kirsten 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):351-363
An instanton method is proposed to investigate the quantum tunneling between two weakly-linked Bose-Einstein condensates confined
in double-well potential traps. We point out some intrinsic pathologies in the earlier treatments of other authors and make
an effort to go beyond these very simple zero order models. The tunneling amplitude may be calculated in the Thomas-Fermi
approximation and beyond it; we find it depends on the number of the trapped atoms, through the chemical potential. Some suggestions
are given for the observation of the Josephson oscillation and the MQST.
Received 29 June 2001 and Received in final form 17 September 2001 相似文献
18.
M. Modugno C. Fort P. Maddaloni F. Minardi M. Inguscio 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):345-349
We have investigated the center-of-mass oscillations of a 87Rb Bose-Einstein condensate in an elongated magneto-static trap. We start from a trapped condensate and we transfer part of
the atoms to another trapped level, by applying a radio-frequency pulse. The new condensate is produced far from its equilibrium
position in the magnetic potential, and periodically collides with the parent condensate. We discuss how both the damping
and the frequency shift of the oscillations are affected by the mutual interaction between the two condensates, in a wide
range of trapping frequencies. The experimental data are compared with the prediction of a mean-field model.
Received 28 May 2001 相似文献
19.
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
20.
N.P. Proukakis P. Lambropoulos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):355-370
We present a consistent second order perturbation theory for the lowest-lying condensed modes of very small, weakly-interacting
Bose-Einstein condensates in terms of bare particle eigenstates in a harmonic trap. After presenting our general approach,
we focus on explicit expressions for a simple three-level system, mainly in order to discuss the analogy of a single condensate
occupying two modes of a trap with the semi-classical theory for two-mode photon lasers. A subsequent renormalization of the
single-particle energies to include the dressing imposed by mean fields demonstrates clearly the consistency of our treatment
with other kinetic approaches.
Received 14 December 2001 相似文献