  We study the dynamics of a one dimensional quantum spin chain evolving from
unentangled or entangled initial state. At a given instant of time a quantum
dynamical process (ex. measurement) is performed on a single spin at one end of
the chain, decohering the system. Through the further unitary evolution, a
signal propagates in the spin chain, which can be detected from a measurement
on a different spin at later times. From the dynamical unitary evolution of the
decohered state from the epoch time, it is possible to detect the occurrence of
the dynamical process. The propagation of the signal for the dynamical process,
and the speed of the signal are investigated for various spin models, viz.
using the Ising, Heisenberg, and the transverse-XY dynamics.
