*International Journal of Theoretical Physics*
** 34**, 1653-1665 (1995)

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

**Mladen Pavicic
**

*Department of Mathematics, University of Zagreb,
GF, Kaciceva 26, POB-217, HR-10001 Zagreb, Croatia; mpavicic@faust.irb.hr; http://m3k.grad.hr/pavicic
*

*Atominstitute of the Austrian Universities,
Schüttelstraße 115, A-1020 Wien, Austria; pavicic@ati.ac.at
*

*Abstract. *
It is shown that one can * preselect with certainty *
photons in the singlet state from a set of completely
unpolarized and independent photons which did not in any way
directly interact with each other i
* without in any way affecting them *.
The result is based on an experiment which puts together two
unpolarized photons from two independent singlet pairs, makes
them interfere in the fourth order on 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 photons coming out from the beam splitter.
One can obtain the expectation value 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
sugest that the Hilbert space is not a * maximal * model
for quantum measurements.

**PACS numbers: **03.65.Bz, 42.50.Wm

**Keywords: **four photon interferometry,
quantum optics, quantum nonlocality, quantum teleportation,
quantum structures, quantum logic.