| Abstract [eng] |
Decades of intensive investigation on optical vortices has led to growing interest in the utilization of orbital angular momentum (OAM) states of light for quantum communication and quantum information processing [2–5]. To this end, the investigation of optical vortex with a full vectorial consideration interacting with an electromagnetically induced transparency (EIT) media has led to the discovery of spatially dependent transparency [21], and polarization state transitions [24] allowing the manipulation of both the OAM property and the spin angular momentum (SAM) property of light related to its polarization state [8]. These studies has been demonstrated in a system with coherently prepared Λ configuration without a static magnetic field to introduce the quantum coherence [25]. However, these studies of vector vortex beams in the EIT-enabled atomic media has not yet been explored in the context of slow-light propagation regime. This work aims to investigate the interaction of optical vector vortices with an EIT-enabled atomic medium, where spatially dependent transparency and polarization-state transitions can be realized in the slow-light propagation regime. We consider an alternative configuration based on a coherently prepared four-level tripod atomic scheme, in which a weak vector vortex beam interacts with the medium in the presence of a strong control beam carrying no orbital angular momentum (OAM). The weak vector vortex beam consists of paired vortex pulses carrying opposite OAM charges, ±l, together with opposite spin angular momentum (SAM) associated with orthogonal circular polarizations of opposite handedness. Meanwhile, the control field is taken to have an arbitrary circular polarization but no OAM charge. In the linear regime, the vortexOAMis mapped onto the atomic medium, giving rise to symmetric azimuthally structured absorption patterns with a strongly suppressed absorption by the control field. For small detunings, complementary spatially dependent amplification and absorption appear for the two circular polarization components. This OAM-structured coherence induces a dynamical anisotropy that influences both the intensity and polarization evolution of the slow-light vortex beam. During propagation, the polarization state evolves periodically among left-handed circular, linear, and right-handed circular polarizations. Once the beam reaches a stationary regime, its ring-shaped intensity profile transforms into a petal-like structure, while the final polarization state stabilizes according to the initial atomic superposition. The rate of these polarization transitions can be tuned through the control-field strength, demonstrating flexible control over slow-light vector vortex dynamics. |
