Atomic Interactions Within Light Channels Boost Cooperative Effects

Researchers A. S. Kuraptsev and I. M. Sokolov of Petersburg Polytechnic University, in collaboration with the Ioffe Institute, have conducted a detailed analysis revealing the significant influence of evanescent waves on collective effects within atomic ensembles positioned in a waveguide. Kuraptsev and colleagues demonstrate that these evanescent modes can dominate the process of cooperative spontaneous decay and fundamentally alter radiation transfer, exceeding the impact of traditional propagating radiation modes. Their quantum microscopic analysis highlights a modification of dipole-dipole interatomic interaction as the key mechanism driving this phenomenon, offering new insights into controlling collective atomic behaviour within waveguide structures and potentially advancing fields such as quantum photonics and information processing. Evanescent mode dominance alters atomic interactions within nanoscale waveguides For ensembles of N two-level atoms confined within a waveguide, the influence of evanescent modes can exceed that of radiation modes by several orders of magnitude when the waveguide’s transverse dimensions approach critical values. Traditionally, achieving such dominance was considered unfeasible due to the rapid spatial decay of evanescent fields. However, this recent work demonstrates that it is now possible, unlocking the potential for controlling collective atomic behaviour even with atoms spaced relatively far apart. Previous approaches to strong coupling and collective effects relied heavily on closely spaced atoms to facilitate strong dipole-dipole interaction, limiting scalability and introducing fabrication challenges. The ability to achieve strong coupling with larger interatomic distances simplifies device design and enhances robustness. Manipulating waveguide geometry allows for precise tailoring of the interaction between evanescent and radiation modes, fundamentally altering radiation transport within nanoscale structures. The interaction within an ensemble of atoms is strongly dependent on the waveguide’s transverse dimension; as this dimension increases, the characteristics of both evanescent and propagating modes change. Analysis reveals that when the waveguide size changes, the attenuation constant of evanescent modes becomes comparable to the spacing between atoms, significantly influencing photon exchange and the total excited state population. Specifically, the attenuation constant dictates how quickly the evanescent field decays away from the waveguide wall, and when this decay rate matches the interatomic distance, resonant energy transfer between atoms becomes highly efficient. This resonant interaction is crucial for establishing strong collective effects. These evanescent modes modify the dipole-dipole interaction between atoms, leading to altered decay rates and radiation patterns. Investigations of atomic ensembles within a waveguide demonstrate that alterations to the waveguide’s cross-section can transition the system from Anderson localization of light to traditional diffusive radiation transfer, a change directly linked to the number of radiation modes able to propagate. Anderson localization, a phenomenon where light becomes trapped due to strong scattering, is suppressed by the dominance of evanescent modes, favouring directed emission. Consequently, evanescent modes can be dominant compared to radiation modes, impacting the lifetimes of collective atomic states and the dynamics of cooperative spontaneous decay. Cooperative spontaneous decay refers to the accelerated decay of an excited atomic ensemble compared to a single isolated atom, and its efficiency is highly sensitive to the surrounding electromagnetic environment. Interpreting the transmission coefficient’s dependence on waveguide size is crucial, particularly near critical points where the number of radiation modes changes. These critical points represent transitions in the waveguide’s ability to support propagating modes, leading to abrupt changes in the radiation environment experienced by the atomic ensemble. Understanding these transitions is essential for optimising waveguide designs for specific applications. Despite the promise of major advances in photonics and quantum technologies, achieving precise control over light-matter interactions at the nanoscale remains a significant hurdle. A lack of detailed characterisation regarding the specific conditions that unlock this dominance hinders broad application of these findings, necessitating further investigation to fully characterise the parameter space where evanescent mode control is most effective. Specifically, the influence of material properties, atomic density, and temperature needs to be explored. Understanding these limitations and optimal conditions will be vital for translating these observations into practical devices. Electromagnetic waves that diminish rapidly from a surface, known as evanescent waves, can fundamentally alter collective atomic behaviour within waveguide structures. A detailed quantum microscopic approach, employed by scientists, demonstrated that these typically overlooked waves can exert a stronger influence than traditional propagating radiation modes under specific conditions. This dominance arises from a modification of the dipole-dipole interaction, allowing control of atomic ensembles even when widely separated, and opens avenues for novel quantum technologies. Potential applications include highly efficient single-photon sources, nanoscale lasers with tailored emission characteristics, and robust quantum memories for quantum information processing. Further research will focus on exploring the scalability of these effects to larger atomic ensembles and developing fabrication techniques to create waveguides with the required precision and control over their geometry. The theoretical framework employed in this study utilises a consistent quantum microscopic approach, allowing for a precise description of the interaction between atoms and the electromagnetic field within the waveguide. This approach accounts for the quantum nature of both the atoms and the photons, providing a more accurate representation of the physical processes involved compared to classical models. The analysis considers the atoms as two-level systems, simplifying the complexity while still capturing the essential physics of cooperative interactions. The waveguide is modelled as a dielectric structure supporting both propagating and evanescent modes, and the interaction between the atoms and these modes is described using Fermi’s Golden Rule, a fundamental principle in quantum mechanics that governs the rate of transitions between quantum states. The resulting equations are then solved numerically to determine the collective atomic behaviour and the characteristics of the emitted radiation. The research demonstrated that evanescent waves within a waveguide can significantly alter how atoms interact with light, sometimes exceeding the influence of traditional radiation. This is because these waves modify the forces between individual atoms, enabling control over larger groups even when physically distant. Scientists used a quantum microscopic approach to analyse these effects on cooperative spontaneous decay, revealing a new understanding of radiation transfer in atomic ensembles. The authors intend to investigate how these findings scale to larger systems and explore methods for precise waveguide fabrication. 👉 More information 🗞 The influence of evanescent waves on the nature of optical cooperative effects in atomic ensembles in a waveguide 🧠 ArXiv: https://arxiv.org/abs/2604.19944 Tags: