  Non-classical states of light field have been exploited to provide marvellous
results in quantum information science. Effectiveness of nonclassical states
depends on whether physical parameter as signal is continuous or digital. Here
we present an investigation on the potential of quasi Bell state of entangled
coherent states in quantum reading of the classical digital memory which was
pioneered by Pirandola. This is a typical example of discrete quantum
discrimination. We show that the quasi Bell state gives the error free
performance in the quantum reading that cannot be obtained by any classical
state.
