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arXiv:2605.28085

Environment-Enhanced Single-Photon Absorption in a Nano-Ring of Dipole-Coupled Quantum Emitters

Eric Sánchez-Llorente, Helmut Ritsch, Maria Moreno-Cardoner

quant-phcond-mat.quant-gasSubmitted May 27, 2026• Announced May 28, 2026• 0 citations
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Abstract

Decoherence is mostly detrimental in quantum information and quantum optics applications. However, the interplay between environment-induced incoherent dynamics and unitary evolution can give rise to novel quantum many-body phenomena that can be harnessed as a useful resource. As is well known, in dense subwavelength atomic arrays only a single collective eigenmode in the single-excitation manifold couples strongly to free-space radiation, exhibiting superradiant spontaneous emission. Most of the remaining eigenstates form a manifold of weakly radiative modes, giving rise to long-lived subradiant excitations. Here we demonstrate that populating these subradiant modes via additional decoherence mechanisms, such as dephasing or coupling to phonons, can significantly enhance single-photon absorption in a nanoring of quantum emitters. Such nanoring geometry is particularly appealing due to its unique optical properties and its resemblance to natural light-harvesting complexes, which serve as efficient antennas in photosynthesis. Our findings may shed light on fundamental aspects of energy absorption in nature; despite the much greater complexity of biological systems, they may nonetheless operate according to similar underlying optical principles.

Comments
18 pages, 9 figures (appendix included); comments welcome

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Decoherence is mostly detrimental in quantum information and quantum optics applications. However, the interplay between environment-induced incoherent dynamics and unitary evolution can give rise to novel quantum many-body phenomena that can be harnessed as a useful resource. As is well known, in dense subwavelength atomic arrays only a single collective eigenmode in the single-excitation manifold couples strongly to free-space radiation, exhibiting superradiant spontaneous emission. Most of the remaining eigenstates form a manifold of weakly radiative modes, giving rise to long-lived subradiant excitations. Here we demonstrate that populating these subradiant modes via additional decoherence mechanisms, such as dephasing or coupling to phonons, can significantly enhance single-photon absorption in a nanoring of quantum emitters. Such nanoring geometry is particularly appealing due to its unique optical properties and its resemblance to natural light-harvesting complexes, which serve as efficient antennas in photosynthesis. Our findings may shed light on fundamental aspects of energy absorption in nature; despite the much greater complexity of biological systems, they may nonetheless operate according to similar underlying optical principles.
Efficient transport and harvesting of excitation energy under low light conditions is an important process in nature and quantum technologies alike. Here we formulate a quantum optics perspective to excitation energy transport in configurations of two-level quantum emitters with a particular emphasis on efficiency and robustness against disorder. We study a periodic geometry of emitter rings with subwavelength spacing, where collective electronic states emerge due to near-field dipole–dipole interactions. The system gives rise to collective subradiant states that are particularly suited to excitation transport and are protected from energy disorder and radiative decoherence. Comparing ring geometries with other configurations shows that the former are more efficient in absorbing, transporting, and trapping incident light. Because our findings are agnostic as to the specific choice of quantum emitters, they indicate general design principles for quantum technologies with superior photon transport properties and may elucidate potential mechanisms resulting in the highly efficient energy transport efficiencies in natural light-harvesting systems.
Nanoscopic arrays of quantum emitters can feature highly sub-radiant collective excitations with a lifetime exponentially growing with emitter number. Adding an absorptive impurity as an energy dump in the center of a ring shaped polygon allows to exploit this feature to create highly efficient single photon antennas. Here among regular polygons with an identical center absorbing emitter, a nonagon exhibits a distinct optimum of the absorption efficiency. This special enhancement originates from the unique emergence of a subradiant eigenstate with dominant center occupation. Only for nine emitters the sum of coupling strengths of each emitter to all others matches the center to the ring coupling. Analogous to a parabolic mirror the antenna ring then concentrates incoming radiation at its center without being significantly excited itself. Similar large efficiency enhancements, which even prevail for broadband excitation, can also be engineered for other antenna sizes by tailoring the frequency and magnitude of the central absorber. Interestingly, for very small structures a quantum treatment predicts an even stronger enhancement for the single photon absorption enhancement than a classical dipole model. As natural light harvesting structures are often based on ring shaped structures, the underlying principle might be exploited there as well.
A ring of dipole-coupled quantum emitters positioned at subwavelength distances possesses only a few radiant but many subradiant collective excitations with lifetimes growing exponentially with the atom number. These exhibit a three-dimensionally confined spatial radiation field pattern and form nanoscale high-QQQ optical resonators. Tailoring size, orientation, and distance between two rings allows for increasing the ratio of coherent ring-to-ring energy transfer versus free-space emission by orders of magnitude. In particular, the more dark and delocalized over several sites are excitons, the higher is their fidelity for transport to a second ring.
Subwavelength arrays of quantum emitters feature unique and largely design-able nonlinear optical properties. As a generic example we study a sub-wavelength sized ring of identical dipoles with an extra identical absorbing emitter at the center. For a 9-ring one finds the most efficient antenna configuration to direct single incoming photons to the center without re-emission. Interestingly, for very tiny structures sizes below a tenth of a wavelength, a full quantum description predicts an even larger absorption enhancement than a mean field model using a classical dipole approximation. We identify the origin of the enhancement in the appearance of a collective dark state with dominant center occupation. By special design of the center absorber one thus can harness the same efficiency enhancement also at different wavelengths and for other geometric structures. On the one hand this idea could be the basis of a new generation of highly efficient and selective nano antennas, while on the other hand, it could be an important piece towards understanding the surprising efficiency of natural light harvesting molecules. Adding gain via active dipoles in such nano ring systems allows to design minimalist laser like classical light sources. In the nonlinear operating regime at stronger pump fields these systems transform to non-classical light sources with tailor-able spatio-temporal emission upon coherent illumination.
We theoretically investigate the collective emission of one and two circular arrays of two-level atoms surrounding an optical nanofiber. We show that the radiation eigenmodes of a single ring selectively couple to specific guided modes of the fiber, according to their symmetry, and study how the physical parameters of the system control their nature. In particular, we identify situations in which the emission toward radiation modes is highly suppressed with respect to fiber-guided modes while the lifetime of the atomic excitation is enhanced. We further address the case of two identical nanorings positioned at a distance from each other along the nanofiber. By contrast to free-space configurations, the rings can exchange excitations even at large separation through nanofiber guided modes resulting in enhanced sub- and super-radiance with respect to the single-ring case. Our findings suggest that the ring configuration is promising for the implementation of efficient and versatile light-matter nanofiber-based interfaces and the achievement of waveguide quantum electrodynamics.
Abstract Ring geometries of subwavelength-spaced quantum emitters exhibit outstanding radiation properties and are useful for antennas, excitation transport, and storage. Taking inspiration from the oligomeric geometry, in particular by considering only the position and dipole orientations of the bacteriochlorophylls in biological light-harvesting 2 complexes of (approximately 6 nm in diameter), we propose and predict highly efficient interlayer excitation transfer, achieving a maximum of 100% transfer for certain choices of dipole orientations in a three-dimensional (3D) concentric stacked ring geometry with C 9 symmetry and a diameter of 400 nm, formed by two-level atoms. Utilizing the quantum optical open system Lindblad master equation approach for estimating the collective dipole dynamics, we demonstrate that, depending on the system parameters, our bio-inspired 3D ring of quantum emitters enables efficient asymmetric excitation transfer between two ring layers, in particular from sparse to dense quantum emitter arrangements. The presented nanoscale geometry is expected to be realizable with diverse physical platforms operating at cryogenic temperatures, where the interacting dipole description remains applicable and, importantly, dominant over environmental decoherence.