Optical vortices of slow light using tripod scheme

We consider propagation, storing and retrieval of slow light (probe beam) in a resonant atomic medium illuminated by two control laser beams of larger intensity. The probe and two control beams act on atoms in a tripod configuration of the light-matter coupling. The first control beam is allowed to have an orbital angular momentum (OAM). Application of the second vortex-free control laser ensures the adiabatic (lossles) propagation of the probe beam at the vortex core where the intensity of the first control laser goes to zero. Storing and release of the probe beam is accomplished by switching off and on the control laser beams leading to the transfer of the optical vortex from the first control beam to the regenerated probe field. A part of the stored probe beam remains frozen in the medium in the form of atomic spin excitations, the number of which increases with increasing the intensity of the second control laser. We analyse such losses in the regenerated probe beam and provide conditions for the optical vortex of the control beam to be transferred efficiently to the restored probe beam.Comment: 2 figure

Storage and retrieval of vector beams of light in a multiple-degree-of-freedom quantum memory

The full structuration of light in the transverse plane, including intensity, phase and polarization, holds the promise of unprecedented capabilities for applications in classical optics as well as in quantum optics and information sciences. Harnessing special topologies can lead to enhanced focusing, data multiplexing or advanced sensing and metrology. Here we experimentally demonstrate the storage of such spatio-polarization-patterned beams into an optical memory. A set of vectorial vortex modes is generated via liquid crystal cell with topological charge in the optic axis distribution, and preservation of the phase and polarization singularities is demonstrated after retrieval, at the single-photon level. The realized multiple-degree-of-freedom memory can find applications in classical data processing but also in quantum network scenarios where structured states have been shown to provide promising attributes, such as rotational invariance

Expanded horizons for generating and exploring optical angular momentum in vortex structures

Spin provides for a well-known extension to the information capacity of nanometer-scale electronic devices. Spin transfer can be effected with high fidelity between quantum dots, this type of emission being primarily associated with emission dipoles. However, in seeking to extend the more common spectroscopic connection of dipole transitions with orbital angular momentum, it has been shown impossible to securely transmit information on any other multipolar basis – partly because point detectors are confined to polarization measurement. Standard polarization methods in optics provide for only two independent degrees of freedom, such as the circular states of opposing handedness associated with photon spin. Complex light beams with structured wave-fronts or vector polarization do, however, offer a basis for additional degrees of freedom, enabling individual photons to convey far more information content. A familiar example is afforded by Laguerre-Gaussian modes, whose helically twisted wave-front and vortex fields are associated with orbital angular momentum. Each individual photon in such a beam has been shown to carry the entire spatial helical-mode information, supporting an experimental basis for sorting beams of different angular momentum content. One very recent development is a scheme for such optical vortices to be directly generated through electronic relaxation processes in structured molecular chromophore arrays. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE)

Vectorial light-matter interaction -- exploring spatially structured complex light fields

Research on spatially-structured light has seen an explosion in activity over the past decades, powered by technological advances for generating such light, and driven by questions of fundamental science as well as engineering applications. In this review we highlight work on the interaction of vector light fields with atoms, and matter in general. This vibrant research area explores the full potential of light, with clear benefits for classical as well as quantum applications

Slow polaritons with orbital angular momentum in atomic gases

Polariton formalism is applied for studying the propagation of a probe field of light in a cloud of cold atoms influenced by two control laser beams of larger intensity. The laser beams couple resonantly three hyperfine atomic ground states to a common excited state thus forming a tripod configuration of the atomic energy levels involved. The first control beam can have an optical vortex with the intensity of the beam going to zero at the vortex core. The second control beam without a vortex ensures the loseless (adiabatic) propagation of the probe beam at a vortex core of the first control laser. We investigate the storage of the probe pulse into atomic coherences by switching off the control beams, as well as its subsequent retrieval by switching the control beams on. The optical vortex is transferred from the control to the probe fields during the storage or retrieval of the probe field. We analyze conditions for the vortex to be transferred efficiently to the regenerated probe beam and discuss possibilities of experimental implementation of the proposed scheme using atoms like rubidium or sodium.Comment: 4 figure