Measurement Method of the Polarization-Entangled States of Biphotons Using a Quantum Tomograph

Statistical analysis was done on the errors of tomographic measurements of polarization-entangled states of biphotons, which are generated by sources based on the effect of spontaneous parametric light down-conversion. The level of quantum fluctuations in the coincidence circuit that are an unremovable source of error in tomographic measurements was analyzed in detail. The density matrix of the quantum polarization state of biphotons in a polarized Bell state was measured by means of a quantum tomograph. Instrumental errors were compared with errors caused by quantum fluctuations. It is shown that there are no hindrances to the creation of a tomographic metrological test station designed for the characterization of sources of spontaneous parametric down-conversion of light that generate polarization-entangled biphotons.