Metastable Bose-Einstein condensate in a linear potential (original) (raw)
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Vortex creation during magnetic trap manipulations of spinor Bose-Einstein condensates
Physical Review A, 2006
We investigate several mechanisms of vortex creation during splitting of a spinor BEC in a magnetic trap controlled by a pair of current carrying wires and bias magnetic fields. Our study is motivated by a recent MIT experiment on splitting BECs with a similar trap, where unexpected fork-like structure appeared in the interference fringes corresponding to interference of two condensates, one with and the other without a singly quantized vortex. It is well-known that in a spin-1 BEC in a quadrupole trap a doubly quantized vortex is produced topologically by a "slow" reversal of bias magnetic field B z . We find that in the magnetic trap considered it is also possible to produce a 4-and 1-quantized vortex in a spin-1 BEC. The latter is possible, for example, during the magnetic field switching-off process. We therefore provide a possible explanation for the unexpected interference patterns in the experiment. We also give an example of the creation of singly quantized vortices due to "fast" splitting, which is a possible alternative mechanism of the interference pattern.
Vortex state structure of a Bose condensate in an asymmetric trap
Physica B-condensed Matter, 2000
Based on an analytic solution of the Gross-Pitaevskii equation in the large-condensate (Thomas-Fermi) limit we determine the structure of a stationary vortex in a Bose-Einstein condensate in a nonaxisymmetric rotating trap. The condensate velocity field has cylindrical symmetry only near the vortex core and becomes intrinsically anisotropic near the condensate boundaries. Rotating the anisotropic trap induces an additional irrotational velocity field even for a vortex-free condensate.
Spinor Bose Condensates in Optical Traps
Physical Review Letters, 1998
In an optical trap, the ground state of spin-1 Bosons such as 23 Na, 39 K, and 87 Rb can be either a ferromagnetic or a "polar" state, depending on the scattering lengths in different angular momentum channel. The collective modes of these states have very different spin character and spatial distributions.
Response of an atomic Bose-Einstein condensate to a rotating elliptical trap
Journal of Physics B, 2005
We investigate numerically the response of an atomic Bose-Einstein condensate to a weakly-elliptical rotating trap over a large range of rotation frequencies. We analyse the quadrupolar shape oscillation excited by rotation, and discriminate between its stable and unstable regimes. In the latter case, where a vortex lattice forms, we compare with experimental observations and find good agreement. By examining the role of thermal atoms in the process, we infer that the process is temperature-independent, and show how terminating the rotation gives control over the number of vortices in the lattice. We also study the case of critical rotation at the trap frequency, and observe large centre-of-mass oscillations of the condensate.
2010
We demonstrate a fast production of large 23Na Bose-Einstein condensates in an optically plugged, magnetic quadrupole trap. A single global minimum of the trapping potential is generated by slightly displacing the plug beam from the center of the quadrupole field. With a dark magneto-optical trap and a simple rf evaporation, our system produces a condensate with N = 10^7 atoms every 17 s. The Majorana loss rates and the resultant heating rates for various temperatures are measured with and without plugging. The average energy of a spin-flipped atom is almost linearly proportional to temperature and determined to be about 60% of the average energy of a trapped atom. We present a numerical study of the evaporation dynamics in a plugged linear trap.
Dynamics of a vortex in a trapped Bose-Einstein condensate
Physical Review A, 2000
We consider a large condensate in a rotating anisotropic harmonic trap. Using the method of matched asymptotic expansions, we derive the velocity of an element of vortex line as a function of the local gradient of the trap potential, the line curvature and the angular velocity of the trap rotation. This velocity yields small-amplitude normal modes of the vortex for 2D and 3D condensates. For an axisymmetric trap, the motion of the vortex line is a superposition of plane-polarized standing-wave modes. In a 2D condensate, the planar normal modes are degenerate, and their superposition can result in helical traveling waves, which differs from a 3D condensate. Including the effects of trap rotation allows us to find the angular velocity that makes the vortex locally stable. For a cigar-shape condensate, the vortex curvature makes a significant contribution to the frequency of the lowest unstable normal mode; furthermore, additional modes with negative frequencies appear. As a result, it is considerably more difficult to stabilize a central vortex in a cigar-shape condensate than in a disc-shape one. Normal modes with imaginary frequencies can occur for a nonaxisymmetric condensate (in both 2D and 3D). In connection with recent JILA experiments, we consider the motion of a straight vortex line in a slightly nonspherical condensate. The vortex line changes its orientation in space at the rate proportional to the degree of trap anisotropy and can exhibit periodic recurrences.
Centrifugal effects in a Bose-Einstein condensate in the time-orbiting-potential magnetic trap
Physical Review A, 1997
Single particle states in the atomic trap employing the rotating magnetic field are found using the full time-dependent instantaneous trapping potential. These states are compared with those of the effective time-averaged potential. We show that the trapping is possible when the frequency of the rotations exceeds some threshold. Slightly above this threshold the weakly interacting gas of the trapped atoms acquires the properties of a quasi-1D system in the frame rotating together with the field. The role of the atom-atom interaction in changing the ideal gas solution is discussed. We show that in the limit of large numbers of particles the rotating field can be utilized as a driving force principally for the center of mass motion as well as for the angular momentum L = 2 normal modes of the Bose condensate. A mechanism of quantum evaporation forced by the rotating field is analyzed.
Rotation of an atomic Bose–Einstein condensate with and without a quantized vortex
Journal of Physics B: Atomic, Molecular and Optical Physics, 2007
We theoretically examine the rotation of an atomic Bose-Einstein condensate in an elliptical trap, both in the absence and presence of a quantized vortex. Two methods of introducing the rotating potential are considered -adiabatically increasing the rotation frequency at fixed ellipticity, and adiabatically increasing the trap ellipticity at fixed rotation frequency. Extensive simulations of the Gross-Pitaevskii equation are employed to map out the points where the condensate becomes unstable and ultimately forms a vortex lattice. We highlight the key features of having a quantized vortex in the initial condensate. In particular, we find that the presence of the vortex causes the instabilities to shift to lower or higher rotation frequencies, depending on the direction of the vortex relative to the trap rotation.
Vortex line and ring dynamics in trapped Bose-Einstein condensates
Physical Review A, 1999
Among the most important phenomena associated with Bose-Einstein condensation BEC is the quantization of vorticity, which is intimately connected with the existence of persistent currents and superfluidity in quantum fluids. Study of quantized vortices has been confined mainly to liquid He II 1, where detailed comparison to mean-field theory is complicated by strong interactions between atoms. However, such considerations are much less important for the recently achieved BEC in atomic vapors 2–5. In this case the condensate can be ...
Method to create a vortex in a Bose-Einstein condensate
Physical Review A, 2002
It has been shown that a vortex in a BEC with spin degrees of freedom can be created by manipulating with external magnetic fields. In the previous work, an optical plug along the vortex axis has been introduced to avoid Majorana flips, which take place when the external magnetic field vanishes along the vortex axis while it is created. In the present work, in contrast, we study the same scenario without introducing the optical plug. The magnetic field vanishes only in the center of the vortex at a certain moment of the evolution and hence we expect that the system will lose only a fraction of the atoms by Majorana flips even in the absence of an optical plug. Our conjecture is justified by numerically solving the Gross-Pitaevskii equation, where the full spinor degrees of freedom of the order parameter are properly taken into account. A significant simplification of the experimental realization of the scenario is attained by the omission of the optical plug.