Continuous-time limit of topological quantum walks
  We derive the continuous-time limit of discrete quantum walks with topological phases. We show the existence of a continuous-time limit that preserves their topological phases. We consider both simple-step and split-step walks, and derive analytically equations of motion governing their behavior. We obtain simple analytical solutions showing the existence of bound states at the boundary of two phases, and solve the equations of motion numerically in the bulk. 
Radhakrishnan Balu, Daniel Castillo, George Siopsis, Christian   Weedbrook
quant-ph