Absence of Anderson Localization of Light in a Random Ensemble of Point Scatterers
The paper by Skipetrov and Sokolov explores the intricate phenomenon of Anderson localization of light, an area of significant interest due to its potential applications in fields like random lasing and quantum information processing. Building upon the foundational work of Anderson in 1958, which established that strong disorder can impede wave propagation by localizing wave-like excitations, this paper challenges the universal applicability of Anderson localization to electromagnetic waves in random media.
Key Findings
The central claim of the paper is that Anderson localization of light does not manifest in a three-dimensional random ensemble of point scatterers when the vector nature of light is fully considered. This contrasts starkly with the common expectation that localized electronic states, observed in disordered solids and other wave phenomena, would extend to light in similar conditions. The authors demonstrate that neglecting the polarization of light—which is essential for understanding its vector character—can lead to an erroneous conclusion that localization occurs within such media. Their detailed analysis suggests that polarization plays a critical role in determining the localization properties of light waves.
Methodology and Approach
Skipetrov and Sokolov employ a model based on resonant point scatterers—immobile two-level atoms with non-degenerate ground and triply-degenerate excited states—to simulate the multiple scattering of light. The Hamiltonian used reflects interactions through the electromagnetic field, where the vector nature of light introduces additional complexity into the scattering process. Through meticulous calculations, including a scaling analysis and density of eigenstates, the absence of Anderson localization was corroborated, especially at high densities where photon-mediated transport was expected.
Implications
The implications of this research are manifold. Practically, it suggests that systems of randomly positioned cold atoms cannot serve as viable platforms for observing Anderson localization of light, given the prominence of dipole-dipole interactions facilitated by the vector nature of electromagnetic fields. Theoretically, it prompts a reassessment of point-scatterer models for describing light behavior in complex photonic media. The findings emphasize the necessity for incorporating polarization considerations into models of multiple light scattering to accurately predict whether localization transitions can occur.
Future Directions
Looking forward, the paper invites researchers to revisit experimental setups and theoretical models to account for polarization effects, particularly in composite media like semiconductor powders or disordered photonic crystals. It also opens avenues for exploring alternative models that group scatterers into clusters, potentially allowing for different organizational dynamics that might support localized states under certain conditions.
In summary, this paper provides a significant insight into the role of vector nature in light wave localization, underlining the importance of considering polarization in theoretical models of disordered media. It underscores a need for tailored studies on complex media and suggests pathways for future theoretical and experimental exploration in the ongoing development of photonic applications.