Vortex creation in Bose-Einstein condensates by laser-beam vortex guiding

Abstract

A technique for vortex creation in trapped Bose– Einstein condensates is suggested: vortices can be excited at the edge of a condensate and guided to the center by a laser beam moving along a spiral trajectory. Numerical simulations demonstrate the suggested technique. Parameter ranges for the method are given. Computer animations illustrate the dynamics of the guided vortices. PACS: 03.75.Fi; 05.30.Jp; 47.32.Ce; 67.70.Vs The creation of vortices and vortex ensembles in Bose– Einstein condensate (BEC) is presently of interest. Various schemes have been suggested for vortex excitation. Most of them are based on the rotation of the magnetic trap in order to impose an angular momentum on the condensate by external force. This rotation could be achieved by rotating the magnetic fields of an anharmonic trap [1], a technique well known for superfluids. The rotation could be also achieved by stirring rotationally the condensate with a laser beam [2]. The latter technique has recently allowed first realization of vortices in Bose–Einstein condensates: (i) in a two-component condensate [3]; (ii) in a single-component condensate [4]. Another proposal is to use optical beams with appropriate intensity distributions to “imprint” a phase distribution onto the condensate [5]. Here we propose a technique to create vortices, and vortex ensembles, by creation at the edge of the condensate and then guiding them into the condensate, by a laser beam. A bluedetuned narrow laser beam (narrower than the condensate) is known to produce a dip of the density of the condensate [6]. Presumably such a laser beam can be used to pin the vortex. If the laser beam moves slowly through the condensate it can drag the pinned vortex and guide it to a desired location. Our proposal is that a laser beam entering the condensate along a spiral path creates vortex pairs at the boundary of the condensate. The laser beam then pins one of the generated vortices and guides it to a desired location of the condensate. We show numerically how one vortex can be brought into the condensate and made to remain at the condensate center after the laser beam is switched off. The technique can be generalized bringing in, one after another, or simultaneously, many vortices into the condensate if manipulating with several laser beams.