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Physics of Wave Phenomena

Effect of polarization deviation of spontaneous parametric down-conversion on the degree of biphoton entanglement

Dmitry N. Frolovtsev, Sergey A Magnitskiy

Published Jul 1, 2017• 8 citations
Publisher

Abstract

Analysis is given to the effect of polarization deviation due to spontaneous parametric downconversion on the states of polarization-entangled photons generated via a cascaded two-crystal geometry with type I phase matching (e−oo).
DOI
10.3103/s1541308x17030049

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A method has been proposed to improve the degree of polarization entanglement of biphotons obtained by means of a double-crystal scheme. The effect of deviation of the polarization of spontaneous parametric down-converted radiation on the degree of polarization entanglement of biphotons has been examined theoretically and experimentally. The dependence of the concurrence as a measure of entanglement on the difference between the pump phases in the nonlinear crystals of the double-crystal scheme has been studied experimentally, and the improvement of the concurrence by a factor of 2.7 has been achieved at the optimal phase difference.
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We consider a new method for the generation of polarization-frequency entangled states of photon pairs. We use a frequency-nondegenerate regime of spontaneous parametric down conversion where the photon pairs (biphotons) are produced with identical polarizations, propagate mostly in the same direction, but differ in frequency. Entanglement is achieved by a coherent superposition of pairs emitted from two nonlinear crystals, with the polarization of the biphotons from the first crystal being changed by a transformer placed between the two crystals. We show that this scheme allows the degree of entanglement to be controlled by the choice of biphoton frequencies.