Towards a time-reversal mirror for quantum systems
  The reversion of the time evolution of a quantum state can be achieved by changing the sign of the Hamiltonian as in the polarization echo experiment in NMR. In this work we describe an alternative mechanism inspired by the acoustic time reversal mirror. By solving the inverse time problem in a discrete space we develop a new procedure, the perfect inverse filter. It achieves the exact time reversion in a given region by reinjecting a prescribed wave function at its periphery. 
Horacio M. Pastawski, Ernesto P. Danieli, Hernan L. Calvo and Luis E.   F. Foa Torres