Bose-Einstein condensates in standing waves: The cubic nonlinear   Schroedinger equation with a periodic potential
  We present a new family of stationary solutions to the cubic nonlinear Schroedinger equation with a Jacobian elliptic function potential. In the limit of a sinusoidal potential our solutions model a dilute gas Bose-Einstein condensate trapped in a standing light wave. Provided the ratio of the height of the variations of the condensate to its DC offset is small enough, both trivial phase and nontrivial phase solutions are shown to be stable. Numerical simulations suggest such stationary states are experimentally observable. 
Jared C. Bronski, Lincoln D. Carr, Bernard Deconinck, and J. Nathan   Kutz