Bose–Einstein Condensation of Atoms and Photons

Abstract

Bose–Einstein condensation has now been observed in diverse physical systems, starting from liquid Helium, excitons, to alkali atoms at nanokelvin temperature. The trapped cold atoms have provided an ideal venue for exploring fascinating ideas, ranging from Kosterlitz–Thouless (KT) phase transition, metal-insulator quantum phase transition to the realization of Abelian and non-Abelian gauge fields and solitonic excitations, in a controlled environment. Here, after a brief introduction to condensation phenomena in free space and trap, we explicate the working of the magneto optical trap, the work horse of the cold-atom laboratories. Subsequently, we illustrate the properties of experimentally realized dark, bright and grey solitons in the cigar shaped Bose–Einstein condensate (BEC). Focusing on a pan-cake type BEC in two dimensions, the basic aspects of the unique vortex excitations on a plane is elaborated, from which the Kosterlitz–Thouless phase transition follows, when the bound vortex–anti-vortex pairs unbind at \(T_{KT}\). We then describe the recent realization of Bose–Einstein condensation of the ubiquitous photons at room temperature. Parametric condition for occurrence of KT phase transition is then obtained for the photon gas.