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International conference on fiber optics and photonics

Continuous-variable Entanglement in Optical Vortex Beams

Shashi Prabhakar, Salla Gangi Reddy, Abdul Rahim Aadhi, P. Chithrabhanu, G. K. Samanta, Ravindra Pratap Singh

Published Jan 1, 2014• 0 citations
Publisher

Abstract

Optical vortices, although being classical, have properties of two-mode entanglement present in quantum states. We have experimentally verified the violation of Bell’s inequality using Wigner distribution function for such beams.
DOI
10.1364/photonics.2014.m4a.83

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Optical beams with topological singularities have a Schmidt decomposition.Hence, they display features typically associated with bipartite quantum systems; in particular, these classical beams can exhibit entanglement.This classical entanglement can be quantified by a Bell inequality formulated in terms of Wigner functions.We experimentally demonstrate the violation of this inequality for Laguerre-Gauss (LG) beams and confirm that the violation increases with increasing orbital angular momentum.Our experimental scheme, which is designed to give directly the parity of the Wigner function, yields negativity at the origin for LG 10 beams, whereas for LG 20 we always get a positive value.
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We calculate the Wigner (quasi)probability distribution function of the quantum optical elliptical vortex (QEV), generated by coupling squeezed vacuum states of two modes. The coupling between the two modes is performed by using beam splitter (BS) or a dual channel directional coupler (DCDC). The quantum interference due to the coupling between the two modes promises the generation of controlled entanglement for quantum computation and quantum tomography. We compute the entanglement of such QEV formed by non-classical radiation field, using Wigner function. We report a critical squeezing parameter above which the entanglement is less for higher vorticity, which is counter intuitive.