Light’s Spin Can Be Mapped Onto Atoms, Reducing Energy Loss

Researchers Dharma P. Permana and colleagues at Vilnius University, in a collaboration between Vilnius University and the Baltic Institute of Advanced Technology, have observed the propagation of optical vector vortices through a coherently prepared four-level atomic system. The atomic medium maps the twisted properties of the light and dynamically alters its intensity and polarization during travel, inducing a unique form of anisotropy. This control over slow-light vector vortex dynamics, tunable via laser strength, represents a key step towards manipulating light in complex ways and could have implications for optical communications and information processing. Controlled atomic superposition enables ultra-slow light and dynamic polarisation manipulation The speed of slow light propagation has been reduced to the order of tens of metres per second, a significant decrease compared with previous observations that lacked strong control field implementation. This achievement utilises a coherently prepared four-level atomic system and vector vortices, light beams possessing a twisting phase, unlocking dynamic control over light’s polarization and intensity, previously unattainable in slow light regimes. Slow light phenomena arise from the constructive interference between the excitation field and the atomic medium, creating a narrow transmission window where the group velocity of light is dramatically reduced. The four-level system employed here is crucial, allowing for coherent population trapping and electromagnetically induced transparency (EIT) which are essential for achieving substantial slow-light effects. Vector vortices, characterised by their orbital angular momentum (OAM), introduce a spatial degree of freedom that can be exploited for encoding and manipulating information. The OAM, denoted by the topological charge l, dictates the helical wavefront structure of the beam. As the beam propagates, the system maps the twisted properties of incoming light and simultaneously induces predictable polarization transitions, cycling between left-circular, linear, and right-circular states. This dynamic polarization control is achieved through the careful design of the atomic level scheme and the application of a strong control laser. The initial coherent superposition of two ground states within the atomic system acts as a ‘seed’ for the polarization rotation, responding to the circular polarization components of the vector vortex. Detailed analysis of susceptibility characteristics revealed pronounced phase dependence in both absorption and dispersion profiles, varying periodically with an azimuthal angle of π for a topological charge of 1. A strong control field at an amplitude of Γ establishes an electromagnetically induced transparency (EIT) window, sharply reducing absorption when a vector vortex beam interacts with the atomic medium. EIT relies on quantum interference effects, creating a pathway for light to propagate through an otherwise opaque medium. At slight detunings of 0.1Γ, complementary spatial patterns of amplification and absorption emerge for the two circular polarization components, inducing a dynamical anisotropy and ultimately transforming the initial ring-shaped intensity into a petal-like structure. This petal-like structure is a direct consequence of the interplay between the OAM of the vector vortex, the atomic coherence, and the spatially varying absorption and dispersion profiles. Although these results confirm slow-light propagation across the transverse plane, current experiments are limited to normalized propagation distances and do not yet demonstrate sustained coherence over distances relevant for practical device applications. Maintaining coherence over extended distances is a significant challenge in slow-light experiments, requiring precise control over environmental factors and atomic system parameters. The use of a four-level tripod atomic system is particularly advantageous. The ‘tripod’ configuration involves two ground states coupled to a single excited state via a probe and control laser, respectively. This arrangement allows for independent control over the atomic coherence and population dynamics, enabling precise manipulation of the light-matter interaction. The vector vortex, consisting of superposed pulse pairs with opposite circular polarizations and orbital angular momentum (OAM) charges ±l, weakly interacts with this atomic medium. The weak interaction is crucial to preserve the coherence of the vector vortex as it propagates through the medium. Enhanced control of slow light and vector vortex polarisation for advanced photonic technologies Advances in communication and computation are increasingly reliant on manipulating light’s properties. A new degree of control over slow light has been achieved, dramatically reducing light’s speed within a special atomic arrangement, alongside vector vortices, light beams with a twisting structure. The behaviour of this system at higher intensities remains unexplored, and future work will investigate this area. The ability to slow down light and simultaneously control its polarization and spatial structure opens up exciting possibilities for developing novel photonic devices. Manipulating vector vortices offers potential benefits for optical communications, as encoding information onto these beams increases data capacity. The OAM of vector vortices provides an additional degree of freedom for multiplexing information, allowing for the transmission of multiple data channels simultaneously on a single beam. This technique, known as orbital angular momentum multiplexing, has the potential to significantly increase the bandwidth of optical communication systems. Precise control over polarization states is vital for quantum computing applications, enabling stronger and more efficient quantum bits, or qubits. Qubits based on the polarization of photons are particularly promising due to their robustness against decoherence. Now, dynamic control over slow light vector vortices is possible, manipulating both polarization and intensity as light travels through an atomic medium. This moves beyond simply observing how twisted light interacts with matter to actively reshaping its properties, opening new avenues for photonic technologies. The ability to dynamically control the polarization of slow-light vector vortices could be used to create highly efficient and robust qubits, paving the way for scalable quantum computing architectures. Furthermore, the observed anisotropy induced by the atomic medium could be exploited for creating novel optical isolators and circulators, essential components in many photonic circuits. The observed effects are dependent on the initial atomic state superposition, offering a pathway to tailor the light-matter interaction for specific applications. Further research will focus on extending the coherence time and propagation distance, as well as exploring the potential for integrating this technology into practical devices. Researchers demonstrated dynamic control over slow light vector vortices within a tripod atomic system, successfully manipulating both their polarization and intensity during propagation. This matters because encoding data onto the orbital angular momentum and polarization of light beams potentially increases the capacity of optical communication systems and offers a route to more robust qubits for quantum computing. By tuning the control field strength, they achieved periodic transitions in polarization states, transforming ring-shaped light into petal-like structures. Future work will concentrate on extending the distance light travels while maintaining these controlled properties, with the aim of integrating this technique into functional photonic devices. 👉 More information🗞 Propagation of optical vector vortices of slow light in a coherently prepared tripod configuration🧠 ArXiv: https://arxiv.org/abs/2603.23097 Tags: