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Journal of the Optical Society of America B

Steering of quantum signals along coupled paths of arbitrary curvature

Constantinos A. Valagiannopoulos

Published Dec 1, 2020• 1 citation

Abstract

Quantum engineering, as a field of research, is currently attracting a huge scientific, funding, and commercial interest. A generic operation behind most of the related device setups is the efficient steering of quantum signals, by channeling or coupling them with specified intensities, to various spatial sections. This work provides several alternative material combinations for a planar guiding configuration, able to squeeze matter waves into tiny apertures while being maximally apt to evanescently couple them. It is also shown that the proposed designs can work under arbitrary curvature by supporting proper resonances, resulting in propagating or standing-wave patterns around them. The signal interaction between straight semiconducting wires and circular rings is demonstrated in layouts that can be used in a variety of components: from beam splitters and quantum memory elements to matter-wave transformers and quantum circuits.

DOI: 10.1364/josab.404394

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The propagation of matter waves in curved geometry is relevant for ion transport, atomtronics and electrons in nanowires. Curvature effects are usually addressed within the adiabatic limit and treated via an effective potential acting on the manifold to which the particles are strongly confined. However, the strength of the confinements that can be achieved experimentally are limited in practice, and the adiabatic approximation often appears too restrictive for realistic guides. Here, we work out a design method for 2D sharply bent waveguides beyond this approximation using an exact inverse-engineering technique. The efficiency of the method is confirmed by the resolution of the 2D nonlinear Schrödinger equation in curved geometry. In this way, we realize reflectionless and ultrarobust curved guides, even in the presence of interactions. Here, the transverse stability is improved by several orders of magnitude when compared to circular guides of similar size.

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