Time-sliced path integrals with stationary states
  The path integral approach to the quantization of one degree-of-freedom Newtonian particles is considered within the discrete time-slicing approach, as in Feynman's original development. In the time-slicing approximation the quantum mechanical evolution will generally not have any stationary states. We look for conditions on the potential energy term such that the quantum mechanical evolution may possess stationary states without having to perform a continuum limit. When the stationary states are postulated to be solutions of a second-order ordinary differential equation (ODE) eigenvalue problem it is found that the potential is required to be a solution of a particular first-order ODE. Similarly, when the stationary states are postulated to be solutions of a second-order ordinary difference equation (O$\Delta$E) eigenvalue problem the potential is required to be a solution of a particular first-order O$\Delta$E. The classical limits (which are at times very nontrivial) are integrable maps. 
Chris M. Field, Frank W. Nijhoff