Increasing the visibility of multiphoton entanglement

The entanglement between the two beams exiting a Mach-Zehnder interferomete r fed two squeezed states involves many photons. We evaluate the degree of this multiphoton entanglement in terms of the excess entropy of the pure st ate at the output. A novel kind of fourth-order correlation function based on homodyne detection is suggested to reveal entanglement. Apart from the v ery low signals regime homodyne-like detection shows a higher fringes visib ility than the measurement of the coincidence counting rate.