Scheme for directly observing the non-commutativity of the position and   the momentum operators with interference
  Although non-commutativity of a certain set of quantum operators (e.g., creation/annihilation operators and Pauli spin operators) has been shown experimentally in recent years, the commu- tation relation for the position and the momentum operators has not been directly demonstrated to date. In this paper, we propose and analyze an experimental scheme for directly observing the non-commutativity of the position and the momentum operators using single-photon quantum in- terference. While the scheme is studied for the single-photon state as the input quantum state, the analysis applies equally to matter-wave interference, allowing a direct test of the position-momentum commutation relation with a massive particle. 
Jong-Chan Lee, Yong-Su Kim, Young-Sik Ra, Hyang-Tag Lim and Yoon-Ho   Kim
quant-ph