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arXiv:1604.07191 · Physical Review A

Generation of polarization-entangled photon pairs in a planar waveguide

Divya Bharadwaj, Krishnan Thyagarajan

Published Dec 6, 2016• 2 citations
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Abstract

In this paper, we show that the polarization-entangled photon pairs can be generated using spontaneous parametric down conversion in a dual periodically poled planar waveguide. The proposed configuration is shown to have efficiencies higher than in the case of bulk crystals with the possibility of ease of collection, like in channel waveguides, with the additional feature of wavelength tunability. We also show that the planar waveguide configuration permits the generation of hyperentanglement in polarization and path degree of freedom, which is not possible in case of channel waveguide. The proposed design should find applications in quantum information processing using integrated quantum optics.

DOI
10.1103/physreva.94.063816

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In this paper, we show that the polarization-entangled photon pairs can be generated using spontaneous parametric down conversion in a dual periodically poled planar waveguide. The proposed configuration is shown to have efficiencies higher than in the case of bulk crystals with the possibility of ease of collection, like in channel waveguides, with the additional feature of wavelength tunability. We also show that the planar waveguide configuration permits the generation of hyperentanglement in polarization and path degree of freedom, which is not possible in case of channel waveguide. The proposed design should find applications in quantum information processing using integrated quantum optics.
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We examine the modal, spectral, and polarization entanglement properties of photon pairs generated in a nonlinear periodically poled two-mode waveguide (one-dimensional planar or two-dimensional circular) via nondegenerate spontaneous parametric down-conversion. Any of the possible degrees of freedom---mode number, frequency, or polarization---can be used to distinguish the down-converted photons while the others serve as attributes of entanglement. Distinguishing the down-converted photons based on their mode numbers enables us to efficiently generate spectral or polarization entanglement that is either narrowband or broadband. On the other hand, when the generated photons are distinguished by their frequencies in a type-0 process, modal entanglement turns out to be an efficient alternative to polarization entanglement. Moreover, modal entanglement in type-II down-conversion may be used to generate a doubly entangled state in frequency and polarization.
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A proposal is made for the generation of polarization-entangled photon pairs from a periodically poled crystal allowing for high collection efficiency, high entanglement, and stable operation. The theory is formulated for colinear propagation for application to waveguides. The key feature of the theory is the use of type II phase matching using both the +1 and -1 diffraction orders of the poling structure. Although these conditions are fairly restrictive in terms of operating parameters, practical operating conditions can be found. For example, we find that a HeNe pump laser may be used for a periodically poled rubidium-doped potassium titanyl phosphate (Rb:KTP) waveguide to yield single mode polarization-entangled pairs. Fidelities of 0.98 are possible under practical conditions.
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