Eur. Phys. J. D (2013) 67: 100
https://doi.org/10.1140/epjd/e2013-30579-6

Regular Article

Biphoton ququarts as either pure or mixed states, features and reconstruction from coincidence measurements

A.M. Prokhorov General Physics Institute, Russian Academy of Science, 38 Vavilova st., Moscow 119991, Russia

^a e-mail: fedorov@ran.gpi.ru

Received: 18 September 2012
Received in final form: 11 February 2013
Published online: 7 May 2013

Abstract

Features of biphoton polarization-frequency ququarts are considered. Their wave functions are defined as functions of both polarization and frequency variables of photons with the symmetry obligatory for two-boson states taken into account. In experiments, biphoton ququarts can display different features in dependence on whether experiments involve purely polarization or (alternatively) polarization-frequency measurements. If in experiments one uses only polarization measurements, the originally pure states of ququarts can be seen as mixed biphoton polarization states. Features of such states are described and discussed in details. Schemes of coincidence measurements for reconstruction of the ququart’s parameters are suggested and described.