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Optics Letters

Electro-optically switchable spatial-mode entangled photon pairs using a modified Mach–Zehnder interferometer

Jasleen Lugani, Sankalpa Ghosh, Krishna Thyagarajan

Published Aug 30, 2012• 13 citations
Publisher

Abstract

In this Letter, we propose and analyze a switchable integrated optical waveguide device employing a modified Mach-Zehnder interferometer, capable of generating nondegenerate, maximally spatial-mode entangled photon pairs. Using an integrated electro-optic phase modulator, we show the possibility of on-demand switching of spatial-mode entangled state from a Φ+ to a Ψ+ state and vice versa. Such a versatile device with the potential of easy manipulation of the "spatial-mode" degree of freedom, should be very interesting in realizing integrated optical chips for quantum information processing.

DOI
10.1364/ol.37.003729

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In this Letter, we propose and analyze a switchable integrated optical waveguide device employing a modified Mach-Zehnder interferometer, capable of generating nondegenerate, maximally spatial-mode entangled photon pairs. Using an integrated electro-optic phase modulator, we show the possibility of on-demand switching of spatial-mode entangled state from a Φ+ to a Ψ+ state and vice versa. Such a versatile device with the potential of easy manipulation of the "spatial-mode" degree of freedom, should be very interesting in realizing integrated optical chips for quantum information processing.
In this paper, we propose an integrated optic waveguide device employing a modified Mach–Zehnder interferometer, capable of generating nondegenerate, hyperentangled photon pairs. The geometry enables multiple (eight) type-II phase-matched spontaneous parametric downconversion processes simultaneously, resulting in a biphoton state, which is simultaneously entangled in polarization and spatial modes. Using an electro-optic phase modulator, we show the possibility of altering modal entanglement without affecting polarization entanglement. Such switchable, maximally entangled photon pairs, entangled in multiple degrees of freedom, should be very useful in various on-chip quantum optics experiments and in the implementation of quantum information protocols employing higher dimensional entanglement.
Integrated quantum optics becomes a consequent tendency towards practical quantum information processing. Here, we report the on-chip generation and manipulation of photonic entanglement based on reconfigurable lithium niobate waveguide circuits. By introducing periodically poled structure into the waveguide interferometer, two individual photon-pair sources with controllable phase-shift are produced and cascaded by a quantum interference, resulting in a deterministically separated identical photon pair. The state is characterized by 92.9% visibility Hong-Ou-Mandel interference. Continuous morphing from two-photon separated state to bunched state is further demonstrated by on-chip control of electro-optic phase-shift. The photon flux reaches ~1.4*10^7 pairs nm-1 mW-1. Our work presents a scenario for on-chip engineering of different photon sources and paves a way to the fully integrated quantum technologies.
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A key ingredient in emerging quantum-enhanced technologies is the ability to coherently manipulate and detect superpositions of basis states. In integrated optics implementations, transverse spatial modes supported by multimode structures offer an attractive carrier of quantum superpositions. Here we propose an integrated dynamic mode converter based on the electro-optic effect in nonlinear channel waveguides for deterministic transformations between mutually non-orthogonal bases of spatial modes. We theoretically show its capability to demonstrate a violation of a Bell-type Clauser-Horne-Shimony-Holt inequality by measuring spatially mode-entangled photon pairs generated by an integrated photon pair source. The proposed configuration, numerically studied for the potassium titanyl phosphate (KTP) material, can be easily implemented using standard integrated optical fabrication technology.