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arXiv:quant-ph/0111033 · Journal of Optics B Quantum and Semiclassical Optics

Superpositions of the orbital angular momentum for applications in quantum experiments

Alipasha Vaziri, Gregor Weihs, Anton Zeilinger

Published Mar 1, 2002• 211 citations
arXivHTMLPDF

Abstract

Two different experimental techniques for preparing and analysing superpositions of Gaussian and Laguerre–Gaussian modes are presented. These involve exploiting an interferometric method in one case and using computer-generated holograms in the other. It is shown that by shifting a hologram with respect to an incoming Gaussian beam, different superpositions of the Gaussian and the Laguerre–Gaussian beam can be produced. An analytical expression connecting the relative phase, the amplitudes of the modes and the displacement of the hologram is given. The application of such orbital angular momenta superpositions in quantum experiments such as quantum cryptography is discussed.

DOI
10.1088/1464-4266/4/2/367

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Two different experimental techniques for preparing and analysing superpositions of Gaussian and Laguerre–Gaussian modes are presented. These involve exploiting an interferometric method in one case and using computer-generated holograms in the other. It is shown that by shifting a hologram with respect to an incoming Gaussian beam, different superpositions of the Gaussian and the Laguerre–Gaussian beam can be produced. An analytical expression connecting the relative phase, the amplitudes of the modes and the displacement of the hologram is given. The application of such orbital angular momenta superpositions in quantum experiments such as quantum cryptography is discussed.
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It is well known that Laguerre-Gaussian (LG) laser beams with orbital angular momentum (OAM), resulting from a phase singularity and created from the readily available Hermite-Gaussian (HG) laser beam, carry the potential for providing an unlimited number of orbital angular momentum states that could be used for enhanced processing of quantum info mation (QI). This paper presents a comprehensive set of experimentation on the fabrication and use of computer generated holograms to create LG beams from the HG profile of an ordinary He-Ne laser and characterization thereof in preparation for QI applications.
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We generated orbital angular momentum in atoms with a spin degree of freedom and coherently transferred it to a light field, which resulted in the generation of a Laguerre-Gaussian (LG) beam. In this method, atoms obtain orbital angular momentum through Larmor precession around the quadrupole field. Successive operations of quadrupole and homogeneous magnetic fields lead to a change of sign in the LG beam or even generation of superposition states of the LG beam with different indexes in real time. Possible applications to control orbital angular momentum of arbitrary photons are also discussed.