Momentum switches
  Certain continuous-time quantum walks can be viewed as scattering processes. These processes can perform quantum computations, but it is challenging to design graphs with desired scattering behavior. In this paper, we study and construct momentum switches, graphs that route particles depending on their momenta. We also give an example where there is no exact momentum switch, although we construct an arbitrarily good approximation. 
Andrew M. Childs, David Gosset, Daniel Nagaj, Mouktik Raha, Zak Webb
quant-ph