We propose a double-$\mathsf{M}$ system of cold atoms for realizing the reversible storage and manipulation of signal fields encoded in degrees of freedom (DOFs) of polarization and orbital angular momentum (OAM). By employing two pairs of counterpropagating controlling fields, we show that the system exhibits dark state polaritons relating to the polarization and propagation direction of the light fields. Through the active operation of the controlling fields in time, stationary light pulses with polarizations and OAM information can be generated due to the tight coupling and balanced competition between the retrieved signal fields, and can be manipulated coherently and all-optically. Another advantage of our proposed scheme is that the two polarization components of the signal field can be decoupled and thus be independently retrieved from the atomic ensemble, and then the scheme can be employed to realize polarization-dependent beam splitting. Such a multiple DOF-dependent scheme could pave the way toward quantum nonlinear optics without a cavity, and could greatly enhance the tunability and capacity for both classical and quantum information processing.
We propose a double-M system of cold atoms for realizing the reversible storage and manipulation of signal fields encoded in degrees of freedom (DOFs) of polarization and orbital angular momentum (OAM). By employing two pairs of counterpropagating controlling fields, we show that the system exhibits dark state polaritons relating to the polarization and propagation direction of the light fields. Through the active operation of the controlling fields in time, stationary light pulses with polarizations and OAM information can be generated due to the tight coupling and balanced competition between the retrieved signal fields, and can be manipulated coherently and all-optically. Another advantage of our proposed scheme is that the two polarization components of the signal field can be decoupled and thus be independently retrieved from the atomic ensemble, and then the scheme can be employed to realize polarization-dependent beam splitting. Such a multiple DOF-dependent scheme could pave the way toward quantum nonlinear optics without a cavity, and could greatly enhance the tunability and capacity for both classical and quantum information processing.
We propose a quantum memory, each subsystem of which is comprised of two double M-type systems of cold atoms, for the first generation of entangled stationary photons (ESPs). Through the active operation of two pairs of counter-propagating controlling fields in time, the reversible transfer of entanglement between photons and atomic ensembles is realized, and the ESPs can be created due to the tight coupling and balanced competition between the corresponding retrieved signal photons. The reduced density matrix in the photon-polarization basis, which provides the lower bound for any purported entanglement, is constructed for discussing the dynamics evolution of the entanglement in terms of the concurrence. We show that the present scheme can be employed for the entangled photons encoded in degrees of freedom (DOFs) of polarization and orbital angular momentum. Such a multiple DOFs dependent scheme, with many benefits over that in a single one, could pave the way toward quantum nonlinear optics without a cavity and could greatly enhance the tunability and capacity for the quantum information processing.
We study the dynamic processes of reversible dual-channel light memory in a double-tripod atomic system by modulating only a pair of counterpropagating control fields in time. We find that two pairs of stationary light pulses (SLPs) can be simultaneously generated when we switch on both control fields after storage. Two incident signal fields in two channels can be released either simultaneously from the same surface of the sample, or at different times from the same or different surfaces of the sample, depending on the time modulation of the two control fields, the time sequence of the input signal fields, and the group velocities of the signal fields propagating in medium, which could be successfully manipulated in each channel. Comparing with the light storage in spin-wave excitations, the SLPs may suffer a little space-dependent diffusion but maintain optical components required for nonlinear optical interactions. These results could be used to study the enhanced low-noises nonlinear interaction between dual-channel SLPs, which can maximize the interaction time. Besides, this scheme could also be explored to design synchronous multitasking information processing during light memory processes at low-light even below single-photon level.
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.
We study a five-level double-tripod system of cold atoms for efficiently manipulating the dynamic propagation and evolution of a quantum probe field by modulating four classical control fields. Our numerical results show that it is viable to transform the quantum probe field into a pair of two-color stationary light pulses mutually coupled through two wave packets of atomic spin coherence. The pair of stationary light pulses can be released either from the sample entrance and exit synchronously or just from the sample exit with a controlled time delay. In addition, the two-color stationary light pulses are immune to the fast decay originating from the higher-order Fourier components of atomic spin and optical coherence, and may exhibit the quantum limited beating signals with their characteristic frequency determined by detunings of the four classical control fields. These results could be explored to design novel photonic devices, such as optical routing, beam splitter, and beat generator, for manipulating a quantum light field.
Summary form only given. Light beams carrying orbital angular momentum (OAM) have attracted a great interest owing to their several applications ranging from the mechanical manipulation of macroscopic particles to the encoding of quantum information [1]. A well-known family of these beams is constituted by Laguerre-Gaussian modes specified by a topological charge ℓ, which gives to the mode a hélicoïdal phase structure and a corresponding OAM per photon equal to ℓħ. The nonlinear interaction of these beams with atomic systems has been investigated via four-wave mixing processes and the corresponding conservation of OAM demonstrated both in cold and thermal atoms [2]. The storage of OAM in cold and thermal atomic ensembles was also previously demonstrated [3].Differently from the previous observations, in this work we demonstrate that the stored OAM of a light beam can be retrieved along a nearly non-collinear direction with a reasonable fidelity. The experiment is performed in cold cesium atoms obtained from a MOT, using a delayed FWM configuration. Light beams with topological charges ℓ=0,1,2,3, produced by a spatial light modulator (SLM) are incident into the medium along the z direction, as shown in the simplified experimental scheme depicted in Fig. 1 (A). The frequency of the beams is resonant with the transition 6S1/2, F=3 - 6P3/2, F=2. The phase structure of the beam carrying OAM is stored into the Zeeman coherence grating induced by the incident writing beams W and W' that form a small angle (~ή between them and have opposite circular polarization. The writing beams are kept on for a period long enough to create a stationary Zeeman coherence grating and then are switched off. After the storage time, a reading beam R, counter-propagating and with opposite circular polarization to the writing beam W, is turned on and the retrieved beam (C), whose propagation direction is determined by the phase matching condition is monitored by a CCD camera. In Fig. 1(B) (a, b) we show images of the incident beams (W) intensity for the cases ℓ=1,2. In Fig. 1B (c, d) the corresponding images of the retrieved C beams. In order to determine the topological charges of the beams we create interference with a reference Gaussian beam. Fig 1(B) (e,f) and (g,h), show the interferograms for the incident (W) and the retrieved (C) beams respectively. Considering the detection geometry we conclude that the incident and retrieved beams carry the same OAM. These results clearly demonstrate that for small angles between W and W' beams, the OAM stored along the z direction can ben retrieved along the non-collinear direction z'. Additional results concerning the conservationof OAM as well as the manipulation of the stored OAM by a magnetic field will also be presented.
We demonstrate a coherent and dynamic beam splitter based on light storage in cold atoms. An input weak laser pulse is first stored in a cold atom ensemble via electromagnetically-induced transparency (EIT). A set of counter-propagating control fields, applied at a later time, retrieves the stored pulse into two output spatial modes. The high visibility interference between the two output pulses clearly demonstrates that the beam splitting process is coherent. Furthermore, by manipulating the control lasers, it is possible to dynamically control the storage time, the power splitting ratio, the relative phase, and the optical frequencies of the output pulses. With further improvements, the active beam splitter demonstrated in this work might have applications in photonic photonic quantum information and in all-optical information processing.