PRESELECTION WITH CERTAINTY OF PHOTONS IN A SINGLET-STATE FROM A SET OF INDEPENDENT PHOTONS

It is shown that one can preselect with certainty photons in the singl et state from a set of completely unpolarized and independent photons which did not in any way directly interact with each other-without in arg way affecting them. The result is based on an experiment which put s together two unpolarized photons from two independent singlet pairs, making them interfere in the fourth order at a beam splitter so as to preselect the singlet state of the other two photons from the pairs, although no polarization measurement has been carried out on the photo ns coming out from the beam splitter. One can obtain the expectation v alue for the correlated state of the former two unpolarized photons in the Hilbert space and therefore write down the singlet state for them , but one apparently cannot infer the state within the Hilbert space. This might suggest: that the Hilbert space is not a maximal model for quantum measurements.