共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Amoruso I. Meccoli A. Minguzzi M. P. Tosi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(3):361-369
We discuss the ground state and the small-amplitude excitations of a degenerate vapour of fermionic atoms placed in two hyperfine states inside a spherical harmonic trap. An equations-of-motion approach is set up to discuss the hydrodynamic dissipation processes from the interactions between the two components of the fluid beyond mean-field theory and to emphasize analogies with spin dynamics and spin diffusion in a homogeneous Fermi liquid. The conditions for the establishment of a collisional regime via scattering against cold-atom impurities are analyzed. The equilibrium density profiles are then calculated for a two-component vapour of 40K atoms: they are little modified by the interactions for presently relevant values of the system parameters, but spatial separation of the two components will spontaneously arise as the number of atoms in the trap is increased. The eigenmodes of collective oscillation in both the total particle number density and the concentration density are evaluated analytically in the special case of a symmetric two-component vapour in the collisional regime. The dispersion relation of the surface modes for the total particle density reduces in this case to that of a one-component Fermi vapour, whereas the frequencies of all other modes are shifted by the interactions. 相似文献
2.
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
3.
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
4.
M.L. Chiofalo M. Polini M.P. Tosi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):371-378
We study the dispersion relation of the excitations of a dilute Bose-Einstein condensate confined in a periodic optical potential
and its Bloch oscillations in an accelerated frame. The problem is reduced to one-dimensionality through a renormalization
of the s-wave scattering length and the solution of the Bogolubov-de Gennes equations is formulated in terms of the appropriate Wannier
functions. Some exact properties of a periodic one-dimensional condensate are easily demonstrated: (i) the lowest band at
positive energy refers to phase modulations of the condensate and has a linear dispersion relation near the Brillouin zone
centre; (ii) the higher bands arise from the superposition of localized excitations with definite phase relationships; and
(iii) the wavenumber-dependent current under a constant force in the semiclassical transport regime vanishes at the zone boundaries.
Early results by Slater [Phys. Rev. 87, 807 (1952)] on a soluble problem in electron energy bands are used to specify the conditions under which the Wannier functions
may be approximated by on-site tight-binding orbitals of harmonic-oscillator form. In this approximation the connections between
the low-lying excitations in a lattice and those in a harmonic well are easily visualized. Analytic results are obtained in
the tight-binding scheme and are illustrated with simple numerical calculations for the dispersion relation and semiclassical
transport in the lowest energy band, at values of the system parameters which are relevant to experiment.
Received 3 December 1999 and Received in final form 22 March 2000 相似文献
5.
We investigate the collective excitations of a one-dimension Bose–Einstein condensate trapped in an anharmonic potential by solving the time-dependent Tonks–Girardeau equation. The governing equations of motions for the low-energy excitations are obtained using variational approaches. The motion of a 1D BEC in a harmonic trap is just like the motion of one particle in a harmonic trap. And quartic distortion of the potential causes the blue-shift and red-shift on the excitation frequency while cube distortion only causes the red-shift. 相似文献
6.
Using the axially-symmetric time-dependent Gross-Pitaevskii equation we study the phase coherence in a repulsive Bose-Einstein condensate (BEC) trapped by a harmonic and an one-dimensional optical lattice potential to describe the experiment by Cataliotti et al. on atomic Josephson oscillation [Science 293, 843 (2001)]. The phase coherence is maintained after the BEC is set into oscillation by a small displacement of the magnetic trap along the optical lattice. The phase coherence in the presence of oscillating neutral current across an array of Josephson junctions manifests in an interference pattern formed upon free expansion of the BEC. The numerical response of the system to a large displacement of the magnetic trap is a classical transition from a coherent superfluid to an insulator regime and a subsequent destruction of the interference pattern in agreement with the more recent experiment by Cataliotti et al. [New J. Phys. 5, 71 (2003)].Received: 20 March 2003, Published online: 30 July 2003PACS:
03.75.-b Matter waves - 03.75.Lm Tunneling, Josephson effect, Bose-Einstein condensates in periodic potentials, solitons, vortices and topological excitations - 03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow 相似文献
7.
M. A. Baranov 《JETP Letters》2000,72(7):385-392
Superfluid phase transition in an atomic Fermi gas confined to a harmonic trap is studied. The critical transition temperature and the temperature dependence and spatial shape of the order parameter are determined. The spectrum and wave functions of single-particle and collective excitations are obtained for a gas in the superfluid phase. The excitation eigenfrequencies exhibit a pronounced temperature dependence, allowing, e.g., identification of the superfluid phase. 相似文献
8.
B. Van Schaeybroeck A. Lazarides 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):329-333
We theoretically study the collective excitations of an ideal gas confined in an isotropic harmonic trap. We give an exact
solution to the Boltzmann-Vlasov equation; as expected for a single-component system, the associated mode frequencies are
integer multiples of the trapping frequency. We show that the expressions found by the scaling ansatz method are a special
case of our solution. Our findings are most useful in case the trap contains more than one phase: we demonstrate how to obtain
the oscillation frequencies in case an interface is present between the ideal gas and a different phase. 相似文献
9.
We predict a direct and observable signature of the superfluid phase in a quantum Fermi gas, in a temperature regime already accessible in current experiments. We apply the theory of resonance superfluidity to a gas confined in a harmonic potential and demonstrate that a significant increase in density will be observed in the vicinity of the trap center. 相似文献
10.
B. Binz D. Baeriswyl B. Douçot 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):69-87
The weak coupling instabilities of a two dimensional Fermi system are investigated for the case of a square lattice using
a Wilson renormalization group scheme to one loop order. We focus on a situation where the Fermi surface passes through two
saddle points of the single particle dispersion. In the case of perfect nesting, the dominant instability is a spin density
wave but d-wave superconductivity as well as charge or spin flux phases are also obtained in certain regions in the space of coupling
parameters. The low energy regime in the vicinity of these instabilities can be studied analytically. Although saddle points
play a major role (through their large contribution to the single particle density of states), the presence of low energy
excitations along the Fermi surface rather than at isolated points is crucial and leads to an asymptotic decoupling of the
various instabilities. This suggests a more mean-field like picture of these instabilities, than the one recently established
by numerical studies using discretized Fermi surfaces.
Received 11 April 2001 and Received in final form 6 September 2001 相似文献
11.
We study an atomic Fermi gas interacting through repulsive contact forces in a one-dimensional harmonic trap. Bethe-ansatz solutions lead to an inhomogeneous Tomonaga-Luttinger model for the low energy excitations. The equations of motion for charge and spin density waves are analyzed both near the trap center and near the trap edges. While the center shows conventional spin-charge separation, the edges cause a giant increase of the separation between these modes. 相似文献
12.
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
13.
We analyse the effects of atom–atom collisions on a collective laser cooling scheme. We derive a quantum master equation which
describes the laser cooling in presence of atom–atom collisions in the weak-condensation regime. Using such equation, we perform
Monte Carlo simulations of the population dynamics in one and three dimensions. We observe that the ground-state laser-induced
condensation is maintained in the presence of collisions. Laser cooling causes a transition from a Bose–Einstein distribution
describing collisionally induced equilibrium, to a distribution with an effective zero temperature. We analyse also the effects
of atom–atom collisions on the cooling into an excited state of the trap.
Received: 18 June 1999 / Revised version: 24 September 1999 / Published online: 10 November 1999 相似文献
14.
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
15.
A. Ben Ali M. Héritier S. Charfi-Kaddour R. Bennaceur 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):53-61
A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate
magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that
the field can induce a time reversal symmetry breaking SDW order coexisting with the superconducting order and can open a
gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity in might be ascribed to this effect.
Received 7 May 1999 and Received in final form 13 August 1999 相似文献
16.
In this paper, the system dealt with consisting of an ultra-cold neutral spin-polarized Fermi gas undergoing rotation (or in the so-called synthetic magnetic field) trapped by an anisotropic harmonic potential in a two and three-dimensional space at zero temperature. Using the so-called Bloch propagator as a tool, we derive exact closed-form expressions for particle density in Fourier space which are valid for an arbitrary particle number confined by a two and three-dimensional rotating anisotropic harmonic trap. Numerical illustrations and discussions are presented. The results can be easily generalized at finite temperatures. The crossover from two-dimensional to the one-dimensional regime is shown to be reflected in the shape of the density distribution in Fourier space at very fast rotating velocity (or at strong synthetic magnetic field). In addition, an exact analytical expression of the elastic scattering factor is found, a quantity of interest used to probe the spatial distribution of the quantum gases. 相似文献
17.
Infinite homogeneous Fermi systems in the degenerate regime are described by the Uehling-Uhlenbeck equation. The eigenvalue problem associated with the linearized collision operator is solved analytically. Initial value problems are studied with the help of the spectral representation of the time evolution operator. The dynamic transport coefficients of the system can then be calculated in the framework of linear response theory. As an example the viscoelastic behaviour of the Fermi liquid is related to the relaxation of a quadrupole deformation in momentum space. In this connection also the coupling of the driving field to 2p-2h excitations will be discussed. The theory is applied to normal liquid3He and to nuclear matter. 相似文献
18.
E. Peik 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(2):179-183
An electrodynamic trap is proposed that stores cold neutral atoms or nonpolar molecules in their ground state as well as in
excited states by means of the quadratic Stark effect. The trap uses an oscillating hexapole field and a superposed static
homogeneous field. The dynamics of an atom in this trap can be described as a harmonic oscillation in a static pseudopotential.
Stability criteria and sample parameters for a number of atomic species are given.
Received: 7 August 1998 / Received in final form: 7 January 1999 相似文献
19.
J.P. Shaffer W. Chalupczak N.P. Bigelow 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):323-330
We present direct measurements of the overall trap loss rate and the fine structure changing collision rate for ultracold
cesium atom confined in a magneto-optical trap over an intensity range of 5 mW/cm2 to 200 mW/cm2. This set of simultaneous measurements allows the accurate extraction and separation of the fine structure changing rate
and the radiative escape rate as these two processes compete with one another to determine the overall trap loss rate.
Received 4 December 1998 and Received in final form 18 March 1999 相似文献
20.
We consider the possible mechanical instability of an ultracold Fermi gas due to the attractive interactions between fermions of different species. We investigate how the instability, predicted by a mean field calculation, is modified when the gas is trapped in a harmonic potential and quantum effects are included.Received: 19 July 2004, Published online: 6 December 2004PACS:
03.75.Ss Degenerate Fermi gases - 03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow 相似文献