  Two remote parties, Alice and Bob initially share some non-maximally
entangled states. Through the entanglement concentration by local operation and
classical communication(LOCC), they may obtain an outcome of maximally
entangled states in the price of decreasing the number of pairs shared by them.
Recently, entanglement concentration have been experimently demonstrated by
post-selection (T. Yamamoto et al, Nature, 421, 343(2003) and Z. Zhao et al,
quant-ph/0301118). Here we give a modified scheme which can be used for the
entanglement concentration without any post selection by using only practically
existing linear optical devices. In particular, a sophisticated photon detector
to distinguish one photon or two photons is not required. Our scheme can be
used to really produce the event-ready maximally entangled pairs through LOCC
provided that the requested raw pairs are supplied deterministically. A
detailed experimental plan with spontaneous parametric down conversion(SPDC) is
shown.

Quantum Physics