Casimir-like force arising from quantum fluctuations in a slow-moving   dilute Bose-Einstein condensate
  We calculate a force due to zero-temperature quantum fluctuations on a stationary object in a moving superfluid flow. We model the object by a localized potential varying only in the flow direction and model the flow by a three-dimensional weakly interacting Bose-Einstein condensate at zero temperature. We show that this force exists for any arbitrarily small flow velocity and discuss the implications for the stability of superfluid flow. 
D. C. Roberts and Y. Pomeau