Controllable double-well optical trap for cold atoms or molecules

In this paper, we propose a novel scheme to form a controllable double-well optical trap for cold atoms or molecules by using a system composed of a binary pi-phase plate and a lens illuminated by a plane light wave. We calculate the intensity distribution of the double-well trap, and study the evolution process of the optical trap from two wells to a single well, and derive the analytical relation between the characteristic parameters of the double-well trap ( including geometric parameters, the intensity distributions, intensity gradients and their curvatures) and the parameters of optical system. We find that our double-well trap can be continuously changed into a single-well trap by moving the pi-phase plate along the x direction, and the relation between the distance of the trapping centers of the two wells and the moving distance of the pi-phase plate is obtained by data fitting. In addition, our double-well scheme is not only simple and convenient, but also has some important and wide applications in the fields of atomic physics, atom optics, molecule optics and quantum optics and so on.