Storage of orbital angular momenta of light via coherent population oscillation

Tunable optical vortex array in a two-dimensional electromagnetically induced atomic lattice

Optical vortex arrays (OVAs) containing multiple vortices have been in demand for multi-channel optical communications and multiple-particle trapping. In this Letter, an OVA with tunable intensity and spatial distribution was implemented all-optically in a two-dimensional (2D) electromagnetically induced atomic lattice (EIL). Such a square lattice is constructed by two orthogonal standing-wave fields in ⁸⁵Rb vapor, resulting in the periodically modulated susceptibility of the probe beam based on electromagnetically induced transparency (EIT). An OVA with dark-hollow intensity distribution based on 2D EIL was observed in the experiment first. This work thus studied the nonlinear 2D EIL process both theoretically and experimentally, presenting, to the best of our knowledge, a novel method of dynamically obtaining and controlling an OVA and further promoting the construction of all-optical networks with atomic ensembles.

Self-amplifying memory based on multiple cascading four-wave mixing via recoil-induced resonance

We report on a new, to the best of our knowledge, type of optical memory that allows for the amplification of the optical signal carrying the stored information during its reading process. The memory mechanism is demonstrated in an ensemble of cold cesium atoms and is based on the multiple parametric four-wave mixing exploring the external atomic degrees of freedom via recoil-induced resonances. We have particularly demonstrated the storage of light carrying orbital angular momentum with a fourfold amplifying factor for the retrieved signal during the reading process. Memory lifetimes of the order of hundreds of microseconds have been measured, and possible applications for this self-amplifying memory are discussed.

Optically Tunable Gratings Based on Coherent Population Oscillation

We theoretically study the optically tunable gratings based on a L-type atomic medium using coherent population oscillations from the angle of reflection and transmission of the probe field. Adopting a standing-wave driving field, the refractive index of the medium as well as the absorption are periodically modified. Consequently, the Bragg scattering causes the effective reflection. We show that different intensities of the control field lead to three types of reflection profile which actually correspond to different absorption/amplification features of the medium. We present a detailed analyses about the influence of amplification on the reflection profile as well. The coherent population oscillation is robust to the dephasing effect, and such induced gratings could have promising applications in nonlinear optics and all-optical information processing.

Controllable population dynamics in Landau-quantized graphene

In this paper, we carry out a theoretical investigation on the population dynamics of graphene system under continuous-wave (cw) laser and chirped pulse excitation. Results of our numerical simulations reveal that complete population transfer from an initially occupied ground state to the initially unoccupied excited states can be achieved by choosing appropriate values of the chirp rate, the laser field intensity and frequency, as well as other system parameters. Also, we observe coherent Rabi-like population oscillations between the initial ground state and the excited final state. It is induced by the combined effect of cw and chirped-pulse laser fields. These results will contribute to the understanding of carrier-carrier and carrier-phonon interactions in graphene system, and may find applications in graphene-based high-speed electronic and optoelectronic devices.

Optical memory based on quantized atomic center-of-mass motion

We report a new type of optical memory using a pure two-level system of cesium atoms cooled by the magnetically assisted Sisyphus effect. The optical information of a probe field is stored in the coherence between quantized vibrational levels of the atoms in the potential wells of a 1-D optical lattice. The retrieved pulse shows Rabi oscillations with a frequency determined by the reading beam intensity and are qualitatively understood in terms of a simple theoretical model. The exploration of the external degrees of freedom of an atom may add another capability in the design of quantum-information protocols using light.

Coherent Population Oscillation-Based Light Storage

We theoretically study the propagation and storage of a classical field in a Λ-type atomic medium using coherent population oscillations (CPOs). We show that the propagation eigenmodes strongly relate to the different CPO modes of the system. Light storage in such modes is discussed by introducing a "populariton" quantity, a mixture of populations and field, by analogy to the dark state polariton used in the context of electromagnetically induced transparency light storage protocol. As experimentally shown, this memory relies on populations and is then-by contrast with usual Raman coherence optical storage protocols-robust to dephasing effects.

Magnetically tuned, robust and efficient filtering system for spatially multimode quantum memory in warm atomic vapors

Warm atomic vapor quantum memories are simple and robust, yet suffer from a number of parasitic processes which produce excess noise. For operating in a single-photon regime precise filtering of the output light is essential. Here, we report a combination of magnetically tuned absorption and Faraday filters, both light-direction insensitive, which stop the driving lasers and attenuate spurious fluorescence and four-wave mixing while transmitting narrowband Stokes and anti-Stokes photons generated in write-in and readout processes. We characterize both filters with respect to adjustable working parameters. We demonstrate a significant increase in the signal-to-noise ratio upon applying the filters seen qualitatively in measurements of correlation between the Raman scattered photons.

Rotation of millimeter-sized objects using ordinary light

The ability to optically rotate bodies offers new degrees of control of micro-objects with applications in various domains, including microelectromechanical systems (MEMS), biomanipulations, or optofluidics. Here we demonstrate the optically-induced rotation of simple asymmetric two-dimensional objects using plane waves originating either from ordinary laser sources or from black body radiation. The objects are floating on an air/water interface. We observe a steady-state rotation depending on the light intensity and on the asymmetry of the object. We interpret this rotation in terms of light diffraction by the edges of the object. Such systems could be easily implemented in optofluidic devices to induce liquid flow without the need for special light sources.

Nonlinear optical memory for manipulation of orbital angular momentum of light

We report on the demonstration of a nonlinear optical memory (NOM) for storage and on-demand manipulation of orbital angular momentum (OAM) of light via higher-order nonlinear processes in cold cesium atoms. A spatially resolved phase-matching technique is used to select each order of the nonlinear susceptibility associated, respectively, with time-delayed four-, six-, and eight-wave mixing processes. For a specific configuration of the stored OAM of the incident beams, we demonstrated that the OAM of the retrieved beam can be manipulated according to the order of the nonlinear process chosen by the operator for reading out the NOM. This demonstration indicates new pathways for applications in classical and quantum information processing where OAM of light is used to encode optical information.