Manipulation of atoms by optical field
Encyclopedia
When cold atoms or a Bose-Einstein condensate (BEC) of an atomic gas is placed in a light standing wave
produced by two counter-propagating lasers of certain frequency, the atoms are diffracted in different order. A cold atom absorbs a photon from one of the laser beams and emits in the other beam receiving a net momentum of
in the direction of the photon. Here 
is the magnitude of the wave vector of the laser. This is called two-photon recoil process. In such situation, a BEC cloud sitting at the center of a trap is split into two identical clouds. The clouds then travel in opposite directions with a velocity, 
in the direction of the photon.
Standing wave
In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...
produced by two counter-propagating lasers of certain frequency, the atoms are diffracted in different order. A cold atom absorbs a photon from one of the laser beams and emits in the other beam receiving a net momentum of
in the direction of the photon. Here is the magnitude of the wave vector of the laser. This is called two-photon recoil process. In such situation, a BEC cloud sitting at the center of a trap is split into two identical clouds. The clouds then travel in opposite directions with a velocity, in the direction of the photon.