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Optics Letters

Generation of hyper-entangled states in strongly coupled topological defects

Nicola Bergamasco, John E. Sipe, Marco Liscidini

Published Apr 12, 2021• 1 citation
Publisher

Abstract

We investigate spontaneous parametric downconversion (SPDC) in a waveguide array supporting two strongly coupled topological guided modes. We show that it is possible to generate photon pairs that are hyper-entangled in energy and path. We study the state robustness against positional disorder of the waveguides, in terms of Schmidt number (SN), fidelity, and density matrix. We show that quantum correlations are in general robust due to the peculiar interplay between structure topology and second-order nonlinear interaction.

DOI
10.1364/ol.425278

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We investigate spontaneous parametric downconversion (SPDC) in a waveguide array supporting two strongly coupled topological guided modes. We show that it is possible to generate photon pairs that are hyper-entangled in energy and path. We study the state robustness against positional disorder of the waveguides, in terms of Schmidt number (SN), fidelity, and density matrix. We show that quantum correlations are in general robust due to the peculiar interplay between structure topology and second-order nonlinear interaction.
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The generation of multi-photon quantum states in integrated waveguiding structures provides a route to the creation of quantum optical chips. In particular, the simultaneous generation of photons through spontaneous parametric down-conversion (SPDC) and their quantum walks in nonlinear waveguide arrays (WGAs) can be used to produce strongly spatially entangled biphoton states [1] with applications for quantum search algorithms [2]. Whereas up to now only arrays of single-mode nonlinear waveguides have been considered for SPDC, in general the waveguides may support several guided modes, which were demonstrated to strongly affect nonlinear wave mixing in the classical regime [3]. Here we show that using higher order modes for SPDC has a significant influence on the generated two-photon states and gives additional means to control them. In particular, we employ the symmetry of the modes to engineer effectively nonlocal photon pair generation by SPDC.
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We present a theoretical study on the generation of photon pairs via spontaneous four-wave mixing in a waveguide array supporting topologically protected guided modes. Following a statistical approach, we introduce incremental levels of disorder in the waveguide positions and analyze the effects in terms of photon path correlations and generation efficiency. For moderate level of disorder, we show that the generated two-photon state as well as the generation rate is preserved. However, we find that for higher level of disorder quantum correlations are significantly affected, despite the fact that the linear properties of the topological mode are still protected.