An arbitrary polarization state of a single-mode biphoton is considered. The operationalistic criterion is formulated for the orthogonality og these states. It can be used to separate a biphoton with an arbitrary degree of polarization from a set of biphotons orthogonal to it. This is necessary fro the implementation of quantum cryptography protocol based on three-level systems. The experimental test of this criterion amounts to the observation of the anticorrelation effect for a biphoton with an arbitraty polarization state.
@article{arxiv.quant-ph/0305113,
title = {Operationalistic Orthogonality Condition for Single-Mode Biphotons (Qutrits)},
author = {A. A. Zhukov and G. A. Maslennikov and M. V. Chekhova},
journal= {arXiv preprint arXiv:quant-ph/0305113},
year = {2007}
}