Quantum quenches as classical critical films

We study the unitary time evolution of the order parameter of a quantum system after a sudden quench in the parameter which drives the transition. By mapping the dynamics onto the imaginary time path integral in a film geometry we derive the full mean-field non-equilibrium phase diagram for a one-component order parameter. The recently discovered non-equilibrium transition is identified with the shifted critical point in films and therefore it is generally expected to occur in more than one spatial dimension. We also find that anharmonic oscillations of the order parameter are a general feature of the mean-field dynamics after the quench.