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Research by Professors Abouraddy, Christodoulides, Saleh et al featured in Optics & Photonics News "Optics in 2013" Special Issue

Entangled photon pairs Entangled photon pairs are generated at a nonlinear crystal[NLCI and imaged onto the input face of the waveguide array. Using a beam splitter [BSI, two copies of the output face of the array are imaged onto the planes of two scanning multi mode fibers connected to single photon counting modules [SPCMlleading to a coincidence circuit. (Inset) The measured photon coincidence maps as functions of the waveguide positions x1 and x2 for Ia I single-waveguide input and lbl multi-waveguide input with photon pairs in a spatially extended entangled correlated state.

An article in Optics & Photonics News titled "Observing Anderson Co-Localization of Entangled Photon Pairs" features Quantum Optics research by Professors Abouraddy, Christodoulides, Saleh et al.

In 1958, Philip Anderson suggested that a quantum mechanical wave function may undergo localization in a disordered lattice as a result of interference between different paths arising from multiple scattering. While direct evidence of this localization remains elusive in solid state physics, its optical analogue may be realized in random arrays of coupled waveguides. The propagation of quantum light in such photonic environments has been theoretically investigated. One of the most interesting predictions of these studies is the possibility of a new type of localization, which occurs when correlated two-photon states-such as Einstein-Podolsky-Rosen entangled photon pairs-are launched in a disordered lattice. We recently demonstrated two-photon Anderson co-localization in a waveguide array.

The array consists of identical, evanescently coupled waveguides, laser-written in silica glass. We varied the inter-waveguide spacing to introduce disorder in the coupling coefficients. Optical spontaneous parametric downconversion was used to produce photon pairs which were imaged onto the waveguide array. Two different two-photon quantum states were considered: 1) a Fock state |2) injected into a single waveguide; and 2) a spatially extended entangled state in which the photon pair is coupled together into any one of these waveguides. The two photons are separated at the output and detected in coincidence to produce a correlation map. It was essential to maintain the Einstein-Podolsky-Rosen spatial entanglement when launching the two photons onto the chip. This is in contrast to previous experiments that stripped spatial entanglement prior to coupling.

When both photons are coupled into a single waveguide, the spatial correlation function at the output is separable and localization of each photon is observed. Alternatively, when the two photons are in the spatially extended entangled state, they emerge from the array with their spatial correlation intact. Neither photon, considered separately (while tracing over the other), localizes in the usual sense. But the pair co-localizes in correlation space, i.e., the photons always exit together from the same waveguide element. It will be interesting to study the effects of quantum entanglement in higher-dimensional random settings where Anderson localization phenomena also occur.

Researchers: A.F. Abouraddy, D.N. Christodoulides, L.A. Martin, B.E.A. Saleh, G. Di Giuseppe, F. Dreisow, R. Keil, S. Nolte, A. Perez-Leija and A. Szameit

Observing Anderson Co-Localization of Entangled Photon Pairs.pdf

Posted Tuesday, December 3, 2013

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