Abstract
We propose methods to generate and manipulate vortex dipoles in an atomic Bose-Einstein condensate using Gaussian beams of red- or blue-detuned laser. Vortex dipoles with controlled velocities are shown to be created and launched by a red-detuned beam and by two blue-detuned beams. Critical beam velocities for the vortex nucleation are investigated. The launched vortex dipoles can be trapped, curved, accelerated, and decelerated by using Gaussian laser beams. Collisions between vortex dipoles are demonstrated.
- Received 7 June 2011
DOI:https://doi.org/10.1103/PhysRevX.1.021003
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Published by the American Physical Society
Popular Summary
A vortex dipole is a pair of vortices with opposite circulations and is commonly found in nature, such as in ocean currents. In superfluids such as liquid helium, which are quantum fluids, vortices with quantized circulations were observed more than 50 years ago, but vortex dipoles have only been observed very recently in more exotic superfluids: low-density Bose-Einstein condensates of cold atoms and a gas of polaritons excited in a semiconductor cavity. So far, both theoretical and experimental studies have focused on the generation of vortex dipoles and the characterization of their dynamics. In this theoretical paper, we expand the basic idea of stirring an atomic Bose-Einstein condensate with a laser beam with a bell-shaped (Gaussian) spatial intensity profile and propose ways of not only creating, launching, trapping, accelerating, decelerating, and curving vortex dipoles, but also doing so with control.
The “laser-beam stirrer” that was used to generate vortex dipoles in an atomic Bose-Einstein condensate previously was “blue detuned,” in that its photon energy was higher than that of the atomic transition. Under appropriate conditions, such a blue-detuned laser beam acted as a bell-shaped repulsive potential for the atoms in the condensate. Our vortex-dipole launcher uses either a moving “red-detuned” laser beam, which acts as a reversed-bell-shaped attractive potential for the atoms, or a pair of moving blue-detuned beams. A comoving pair of red-detuned beams turn out to act as a vortex-dipole trap. Placing a blue- or red-detuned Gaussian laser beam near the trajectory of a launched vortex dipole can bend the trajectory toward the beam or away from it. Turning a Gaussian beam on the trajectory of a moving vortex dipole can accelerate or decelerate it.
Backed by numerical simulations that describe situations that are experimentally realizable, we are confident that our work increases considerably the range of experiments and will lead to more, and more precise, understanding of dynamic properties of vortex dipoles in superfluids.
