I have given a brief explaination of the ZWM study and a modified apparatus below, but for those wishing to become more familiar with the ZWM study the actual references are (experimental paper first and theoretical second) X. Y. Zou, L. J. Wang, and L. Mandel, Phys. Rev. Lett. 67, 318 (1991). L. J. Wang, X. Y. Zou, and L. Mandel, Phys. Rev. A 44, 4614 (1991). Possibly Mandel's finest work. Two figures are attached, one is the ZWM apparatus and its explaination is as follows: The pump beam goes to the 50/50 beamsplitter (BS) and then pumps one of two downconversion crystals (DC1 and DC2) which transform the photon into two photons (signal and idler) with each having roughly half the frequency/energy. The idler from DC1 is forced to transmit through the DC2 crystal so that it retains coherence between the output of the two crystals. The two signal outputs from DC1 and DC2 are combined at a detector Ds. There are two types of interference here, first is the interference in the coincidence counter (CC). When one of the optical paths is varied there is interference as a function of the combined phases (φs + φi). The coincidence interference results from indistinguishability between the combined pathways from DC1 to Ds and Di -or- from DC2 to Ds and Di. We cannot tell which way the pump photon went after the beam splitter. The second interference occurs at detector Ds and is a simple function of the phase. The interference that occurs at this detector is a lower order. It is simply the indistinguishability between the optical paths from the pump photon to detector Ds. If the detector has a count you cannot tell if it came from DC1 or DC2 depending on which path it took after the beam splitter. The coincidence interference(4th order) requires that all four optical paths to the two detectors be identical (or at least differing by no more than a coherence length). The interference at Ds (2nd order) requires the two optical paths from BS to DC1 to Ds and from BS to DC2 to Ds be identical. By placing the neutral density filter (NDF) between DC1 and DC2 in the idler path i1, the interference at detector Ds vanishes. Why? Because the paths to Ds from the pump are now distinguishable. How? If the pump photon goes to DC1 and downconverts then the signal will go to Ds but the idler will be attenuated by the filter and you will not get a coincidence count at Di. If the pump photon goes to DC2 and downconverts then the signal will go to Ds and the idler will go to Di and there will be a coincidence count. So the presence or non-presence of a coincidence count at Di is the measurement which will determine whether the pump photon went to DC1 or DC2 to downconvert. So by inserting the NDF into the idler path, Mandel has eliminated the interference at detector Ds. And it is worth noting that the interference effect at Ds can only be negated by a distinguishability measurement which occurs at a second detector Di which is spatially separated from Ds, and that these measurements don’t actually need to be made to negate the interference. Mandel notes that these measurements at Di need only be in principle possible to negate the interference pattern. He got the same results without even making the distinguishing measurements. Absolutely Brilliant! Now look at how we modify this to create instant communication. The second figure is for my modified ZWM apparatus and its explaination is as follows: In the Modified ZWM we make the simple change in the positioning of the filter, and instead of analysing the interference at Ds we look at the interference at detector Di by modulating the optical path length between DC1 and DC2 with a modulator (PM). This modulates the pathlength from BS to DC1 to Di relative to the pathlength of BS to DC2 to Di. The question is, is there interference at detector Di like there was at Ds? Interestingly enough, Mandel referred to this detector as “superfluous” to the detection at Ds. This implies that there is interference at Di but this is not a thorough analysis. In the ZWM paper, Mandel does the combined field amplitude for the three fields (pump signal and idler) at the crystal in order to arrive at a counting rate for the coincidence effect and a counting rate for the detector Ds. No analysis is given for the counting rate at Di. If I am correct, and there is an additional interference effect (2nd order) at Di then this interference can be negated with the filter being placed in the s1 path near Ds. By minimising the distance between the filter (NDF) and Ds, and maximising the distance between Ds and Di, such that the latter is much greater than the former, we would be negating the interference effect at Di instantaneously byattenuating the s1 path with the NDF. If all my reasoning is sound up to here then we are a small step away from modulation between the extreme cases (insertion of the NDF and non-insertion) to produce a modulation of the interference at Di. Instant communication. Where have I gone wrong this time?