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1.
对囚禁在轴对称谐振势阱中的玻色凝聚气体,提出一种新的试探波函数,运用Gross-Pitaevskii(G-P)平均场能量泛函和变分的方法,得到玻色凝聚气体基态和单涡旋态波函数的解析表达式,并计算出凝聚原子的平均能量、原子云轴向和径向尺度比,以及产生单涡旋态的临界角速度等重要物理量与凝聚原子数N之间的关系.其结果与Dalfovo等人直接数值求解G-P方程所得到的结果相一致.
关键词:
玻色凝聚气体
G-P泛函
波函数
谐振势阱 相似文献
2.
We investigate the structure of trapped Bose-Einstein condensates (BECs) with long-range anisotropic dipolar interactions. We find that a small perturbation in the trapping potential can lead to dramatic changes in the condensate's density profile for sufficiently large dipolar interaction strengths and trap aspect ratios. By employing perturbation theory, we relate these oscillations to a previously identified "rotonlike" mode in dipolar BECs. The same physics is responsible for radial density oscillations in vortex states of dipolar BECs that have been predicted previously. 相似文献
3.
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
4.
We study the formation of vortices in a dipolar Bose–Einstein condensate in a synthetic magnetic field by numerically solving the Gross–Pitaevskii equation. The formation process depends on the dipole strength, the rotating frequency, the potential geometry, and the orientation of the dipoles. We make an extensive comparison with vortices created by a rotating trap, especially focusing on the issues of the critical rotating frequency and the vortex number as a function of the rotating frequency. We observe that a higher rotating frequency is needed to generate a large number of vortices and the anisotropic interaction manifests itself as a perceptible difference in the vortex formation. Furthermore, a large dipole strength or aspect ratio also can increase the number of vortices effectively. In particular, we discuss the validity of the Feynman rule. 相似文献
5.
We consider rotational motion of an interacting atomic
Bose-Einstein condensate (BEC) with both two- and three-body
interactions in a quadratic-plus-quartic and harmonic-plus-Gaussian
trap. By using the variational method, the influence of the
three-body interaction and the anharmonicity of the trap on the
lowest energy surface mode excitation and the spontaneous shape
deformation (responsible for the vortex formation) in a rotating BEC
is discussed in detail. It is found that the repulsive three-body
interaction helps the formation of the vortex and reduces the lowest
energy surface mode frequency and the critical rotational frequency
of the system. Moreover, the critical rotational frequency for the
vortex formation in the harmonic-plus-Gaussian potential is lower
than that in the quadratic-plus-quartic potential. 相似文献
6.
7.
Vortex formation in a stirred bose-einstein condensate 总被引:1,自引:0,他引:1
Using a focused laser beam we stir a Bose-Einstein condensate of 87Rb confined in a magnetic trap and observe the formation of a vortex for a stirring frequency exceeding a critical value. At larger rotation frequencies we produce states of the condensate for which up to four vortices are simultaneously present. We have also measured the lifetime of the single vortex state after turning off the stirring laser beam. 相似文献
8.
Results on investigation of vortex unstable breakdown are presented. The structure of vortex multiplets was visualized in
a vertical cylindrical container made of transparent organic glass of the optic quality with the inner diameter of 288 mm
and rotating upper lid. Visualization was performed for different heights of this cylinder. The working liquid was 80-percent
water-glycerin mixture, and small air bubbles were used as the tracers. The lid was rotated with a constant angular velocity
under the studied conditions, and air was accumulated in the zones of decreased pressure on axes of vortices. Visualization
of flow structure for unstable swirl flows and cylinder aspect ratios from 3.2 to 5.5 allowed first identification of these
regimes as multispiral breakdowns with formation of helical-like vortex duplets, triplets, and quadruplets. 相似文献
9.
F. V. Kusmartsev 《Czechoslovak Journal of Physics》1996,46(1):31-32
We propose very general vortex nucleation mechanisms[1] analogous to a hydrodynamic instability and calculate associated critical velocity in agreement with experiments. The creation of vortices via extrinsic mechanism is driven by a formation of the surface vorticity sheet created by the flow, which reaches a critical size. Such a sheet screens an attraction of a half-vortex ring to the wall, the barrier for the vortex nucleation disappears and the vortex nucleation is started. In the intrinsic mechanism the creation of a big vortex ring, which transforms into the vortex, is driven by a fluctuative generation of small vortex rings. 相似文献
10.
F. V. Kusmartsev 《Czechoslovak Journal of Physics》1996,46(Z1):31-32
We propose very general vortex nucleation mechanisms[1] analogous to a hydrodynamic instability and calculate associated critical
velocity in agreement with experiments. The creation of vortices via extrinsic mechanism is driven by a formation of the surface
vorticity sheet created by the flow, which reaches a critical size. Such a sheet screens an attraction of a half-vortex ring
to the wall, the barrier for the vortex nucleation disappears and the vortex nucleation is started. In the intrinsic mechanism
the creation of a big vortex ring, which transforms into the vortex, is driven by a fluctuative generation of small vortex
rings.
Work supported by NORDITA and Landau Institute 相似文献
11.
We show that, in the Thomas-Fermi regime, the cores of vortices in rotating dilute Bose-Einstein condensates adjust in radius as the rotation velocity, Omega, grows, thus precluding a phase transition associated with core overlap at high vortex density. In both a harmonic trap and a rotating hard-walled bucket, the core size approaches a limiting fraction of the intervortex spacing. At large rotation speeds, a system confined in a bucket develops, within Thomas-Fermi, a hole along the rotation axis, and eventually makes a transition to a giant vortex state with all the vorticity contained in the hole. 相似文献
12.
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
13.
14.
This paper addresses the drag force and formation of vortices in the boundary layer of a Bose-Einstein condensate stirred by a laser beam following the experiments of Phys. Rev. Lett. 83, 2502 (1999)]. We make our analysis in the frame moving at constant speed where the beam is fixed. We find that there is always a drag around the laser beam. We also analyze the mechanism of vortex nucleation. At low velocity, there are no vortices and the drag has its origin in a wakelike phenomenon: This is a particularity of trapped systems since the density gets small in an extended region. The shedding of vortices starts only at a threshold velocity and is responsible for a large increase in drag. This critical velocity for vortex nucleation is lower than the critical velocity computed for the corresponding 2D problem at the center of the cloud. 相似文献
15.
Scott RG Martin AM Fromhold TM Bujkiewicz S Sheard FW Leadbeater M 《Physical review letters》2003,90(11):110404
We study the dynamics of Bose-Einstein condensates in an optical lattice and harmonic trap. The condensates are set in motion by displacing the trap and initially follow simple semiclassical paths, shaped by the lowest energy band. Above a critical displacement, the condensate undergoes Bragg reflection. For high atom densities, the first Bragg reflection generates a train of solitons and vortices, which destabilize the condensate and trigger explosive expansion. At lower densities, soliton and vortex formation requires multiple Bragg reflections, and damps the center-of-mass motion. 相似文献
16.
We study surface modes of the condensate in the presence of a rotating thermal cloud in an axisymmetric trap. By considering collisions that transfer atoms between the condensate and the noncondensate, we find that m>0 modes, which rotate in the same sense as the thermal cloud, damp less strongly than m<0 modes, where m is the polarity of the excitation. We show that above a critical angular rotation frequency, equivalent to the Landau stability criterion, m>0 modes become dynamically unstable, leading to the possibility of vortex nucleation. We also generalize our stability analysis to treat the case where the stationary state of the condensate already possesses a single vortex. 相似文献
17.
The acoustical response of a slit with a mean bias flow is numerically studied. By means of a potential flow model based on the discrete vortex method and a spanwise-averaged three-dimensional Green?s function, both unsteady vortical flow and slit impedance are obtained in a unified theoretical framework. The numerical simulation focuses on the acoustic-excited vortex structures of the slit flow while neglecting the viscous damping effect. Three representative flow features are demonstrated, which are the destabilized jet flow, the rolling up of vortex sheets and formation of vortex pairs, and the reversal flow with alternating vortex shedding on both sides of the slit. These features are corresponding to low, moderate, and high sound amplitude, respectively. The acoustic behavior of the slit can be divided into linear, transition, and nonlinear regimes. During its evolution through the three regimes, the resistance exhibits a constant value, a slight decrease, and a significant increase with the increasing sound amplitude. Correspondingly, the reactance first remains constant and then shows a modest decrease as the sound amplitude increases. The nonlinear effect also causes the gradual decrease of the mean bias velocity in company with the marked increase of the amplitude of the fluctuating velocity in the slit. The mean bias velocity decreases to about 80 percent of its linear value at the transition point where reversal flow begins to occur, and further decreases to only 10 percent in the highly nonlinear region. The slit impedance is also presented as a function of frequency and for different aspect ratios. And the effects of frequency and slit geometry are discussed. 相似文献
18.
A. Leo G. Grimaldi A. Nigro S. Pace N. Verellen A.V. Silhanek W. Gillijns V.V. Moshchalkov V. Metlushko B. Ilic 《Physica C: Superconductivity and its Applications》2010,470(19):904-906
We study the influence of artificial pinning centers on the vortex critical velocity in Al thin films deposited on top of a periodic array of Permalloy (FeNi) square rings. We demonstrate that the field dependence of the flux flow velocity strongly depends on the particular magnetic state of the rings. In particular, we find that, even when the rings are in a flux closure state, i.e. with little stray field, the vortex critical velocity shows a non-monotonic magnetic field dependence. This behaviour is in sharp contrast with the results obtained in a reference plain film, with no rings underneath. A comparison with the intrinsic strong pinning Nb films previously studied, suggests an interpretation in terms of a channel-like motion of vortices, here induced by the artificial pinning structure. 相似文献
19.
We describe a novel effect related to the controlled birth of a single Josephson vortex. In this phenomenon, the vortex is created in a Josephson transmission line at a T-shaped junction. The "baby" vortex arises at the moment when a "mother" vortex propagating in the adjacent transmission line passes the T-shaped junction. In order to give birth to a new vortex, the mother vortex must have enough kinetic energy. Its motion can also be supported by an externally applied driving current. We determine the critical velocity and the critical driving current for the creation of the baby vortices and briefly discuss the potential applications of the found effect. 相似文献
20.
We perform Monte Carlo studies of vortices in three dimensions in a cylindrical confinement, with uniform and nonuniform density. The former is relevant to rotating 4He; the latter is relevant to a rotating trapped Bose-Einstein condensate. In the former case, we find dominant angular thermal vortex fluctuations close to the cylinder wall. For the latter case, a novel effect is that at low temperatures the vortex solid close to the center of the trap crosses directly over to a tensionless vortex tangle near the edge of the trap. At higher temperatures an intermediate tensionful vortex liquid located between the vortex solid and the vortex tangle may exist. 相似文献