The EPR effect, for a bipartite pure quantum system, is that “as a consequence of two different measurements performed upon the first system, the second system may be left in states with two different wavefunctions.” In a recent work [Phys. Rev. Lett. 98, 140402 (2007)] we provided an operational definition of this effect that works also for mixed states. Here we apply this concept to a split single photon state (|1,0>+|0,1>)/?2. Using only homodyne detection it seems impossible to violate a Bell inequality with this state. However, it is possible to demonstrate the EPR effect, even with substantial vacuum admixture.
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