  We analyze the nonlinear optical response of a five-level system under a
novel configuration of electro-magnetically induced transparency. We show that
a giant Kerr nonlinearity with a relatively large cross-phase modulation
coefficient that occurs in such system may be used to produce an efficient
photon-photon entanglement. We demonstrate that such photon-photon entanglement
is practically controllable and hence facilitates promising applications in
quantum information and computation.
