Polarization Coherence and Entanglement

Preeti Sharma, Nishant Kumar Pathak, Bhaskar Kanseri

We theoretically study the polarization entanglement and the non-local correlations manifested by biphotons using measures as concurrence and CHSH Bell test, generated in the spontaneous parametric down-conversion (SPDC) process for partially spatially coherent pump, affected by the spatial walk-off effects of the extraordinary beam. The study has been carried out for a well-known scheme for generating polarization entanglement utilizing non-collinear, frequency degenerate SPDC process in paired type-I uniaxial crystals. It is found that the polarization entanglement changes drastically with variation in spatial coherence of the pump, offering a possibility to realize a tunable source of polarization entanglement. The study reveals the overriding role of aperture size in compensation of the effect of spatial coherence of pump on the polarization entanglement and non-local correlations, especially in the conservation of polarization entanglement for incoherent and partially coherent pump beams. Free-space quantum secure communication utilizing these quantum states possessing maximal entanglement and partially spatially coherent properties would essentially offer robustness to the losses on propagation through atmospheric turbulence, resulting in a significant enhancement in the key rate.

Natalia Korolkova

José Antonio Fornés

João Batista Rosa Silva, Rubens Viana Ramos

This work discuss the entanglement and quantum polarization of superpositions of two-mode coherent states. We use the concurrence to measure their entanglements and the quantum Stokes parameters and the Q function in order to analyze their polarization and degree of polarization.

S. Asokan, J. Solomon Ivan

Gaussian spatial-polarization entanglement in a coherent vectorial paraxial light field is studied. Detection of spatial-polarization entanglement through fringe movement on rotation of a linear polarizer, with the light field passing through the polarizer, is outlined. The fringe movement is shown to be a sufficient condition for the detection of spatial-polarization entanglement in coherent paraxial vector light fields. Two Gaussian light fields with a small relative tilt but with significant spatial overlap and with orthogonal polarizations are shown to possess close to 1 ebit of spatial-polarization entanglement. Tunable Gaussian spatial-polarization entanglement is experimentally demonstrated in a folded Mach-Zehnder interferometer.