Momentum transfer for momentum transfer-free which-path experiments
  We analyze the origin of interference disappearance in which-path double aperture experiments. We show that we can unambiguously define an observable momentum transfer between the quantum particle and the path detector and we prove in particular that the so called ``momentum transfer free'' experiments can be in fact logically interpreted in term of momentum transfer. 
Aurelien Drezet, Andreas Hohenau, Joachim R. Krenn