  Dynamical phase transition in quantum many body systems is usually studied by
taking it in the ground state and then quenching a parameter to a new value. We
investigate here the dynamics when one performs the time evolution of a generic
state and observe that the rate function related to the Loschmidt echo shows
non-analytic behavior of two types, one related, and the other unrelated, to
the appearance of a quantum phase transition. Specifically, we consider a
quantum Ising chain in an initial configuration which is a generic
superposition of the eigenstates, and follow its dynamics under the transverse
Ising Hamiltonian with constant field. Depending on the the configuration of
the initial state, some singularities appear in the rate function which do not
correspond to the equilibrium phase transition of the Hamiltonian. However
another class of singularity is found having connection with the quantum
critical point. Some features of the singularities of the rate function have
been derived analytically and it is observed that the occupancy of
quasiparticle eigenstates plays the key role in triggering the
non-analyticities.

Statistical Mechanics;Quantum Physics