Optics Express

Unconventional bound states in the continuum

Xue-jian Sun, WenXiao Liu, Hui-Juan Xu, Yakun Cai, Yan-Xia Xu, Hui-Zhong Ma

Published Jul 24, 2026• 0 citations

Abstract

We investigate the influence of long-range hoppings in a structured photonic bath on atom-photon interactions. Considering a system comprising a two-leg giant atom coupled to an extended Su-Schrieffer-Heeger (SSH) model incorporating beyond-nearest-neighbor hoppings while preserving chiral symmetry, we demonstrate the formation of an unconventional bound state in the continuum (BIC) when the atomic transition frequency resonates with a mode inside the propagation band. In particular, the spatial distribution of the photoinc wavefunction of the BIC can be modified by the long-range hoppings. Consequently, when multiple identical giant atoms are included in the system, the resulting decoherence-free interactions between them are rendered less sensitive to the specific topological configuration (e.g., braided, separated, or nested) of the emitters. Furthermore, we propose two efficient and controllable quantum state transfer protocols enabled by the extended SSH model coupled to normal atoms. We show that by appropriately engineering the long-range hopping strengths, perfect excitation transfer can be achieved between two atoms coupled to the edge sites of an infinite SSH chain. In a second scheme, a single atom coupled to the center of a finite SSH chain can transfer its excitation to one of the topological edge modes. Our paper provides a method for controlling atom-photon interactions with significant implications for quantum information transfer and processing.

DOI: 10.1364/oe.607466

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