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Conservation of orbital angular momentum of light in coherent four-wave mixing in cold atoms

K R. T'obosn

Published Jan 1, 2003• 0 citations
OpenAlex

Abstract

respectively. These observed results show that signal and generated beams have topological charge with the same magnitude and sign. Therefore, since they propagate in opposite directions, they should carry opposite OAM, thus demonstrating the conservation of OAM within the light modes involved in this process. Similar results were obtained for a single charge signal beam. Our results present a first step towards the storage of a multidimensional quantum state in a long-lived atomic coherence, a subject that presents a considerable actual interest.

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Non-collinear retrieving of stored orbital angular momentum of light in cold atoms

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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.

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Demonstration of orbital angular momentum conservation in coherent Four-Wave mixing in cold atoms

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We report on the generation of light carrying orbital angular momentum through Bragg diffraction into an electromagnetically induced coherence grating in a degenerate two-level system of cold cesium atoms, demonstrating the c onservation the c onservation of orbital angular momentum of light in a coherent four-wave mixing process. The induced Zeeman coherence grating is shown to contain the spatial phase structure of the incident beams. The e xchange of phase information between a light beam with orbital angular momentum and a long-lived atomic coherence opens up the way to process quantum process information encoded in a multidimensional state space.

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Storage of orbital angular momenta of light via coherent population oscillation

A. J. F. de Almeida, S. Barreiro, W. S. Martins +4 more

We report on the storage of orbital angular momenta (OAM) of light via the phenomenon of coherent population oscillation (CPO) in cold cesium atoms. The experiment is performed using a delayed four wave mixing configuration, where the transverse optical information of a probe field carrying OAM associated with its azimuthal phase dependence is stored in the CPO of Zeeman sublevels of the hyperfine transition F=3→F'=2 of the cesium D2 line. We also demonstrate experimentally the simultaneous storage and retrieval of different OAM states propagating along different directions in space, leading to algebraic operations with OAM and, therefore, opening the possibility of multiplexing OAM states.

arXiv:1505.06618•Optics Letters•May 21, 2015•22 citations
respectively. These observed results show that signal and generated beams have topological charge with the same magnitude and sign. Therefore, since they propagate in opposite directions, they should carry opposite OAM, thus demonstrating the conservation of OAM within the light modes involved in this process. Similar results were obtained for a single charge signal beam. Our results present a first step towards the storage of a multidimensional quantum state in a long-lived atomic coherence, a subject that presents a considerable actual interest.
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 report on the generation of light carrying orbital angular momentum through Bragg diffraction into an electromagnetically induced coherence grating in a degenerate two-level system of cold cesium atoms, demonstrating the c onservation the c onservation of orbital angular momentum of light in a coherent four-wave mixing process. The induced Zeeman coherence grating is shown to contain the spatial phase structure of the incident beams. The e xchange of phase information between a light beam with orbital angular momentum and a long-lived atomic coherence opens up the way to process quantum process information encoded in a multidimensional state space.
Abstract The coherent control of orbital angular momentum four-wave mixing (OAM-FWM) signal in a cascaded three-level atomic system by multiple parameters of incident lights is studied. Firstly, based on the Laguerre–Gaussian beam, the expressions for the intensity and phase of the FWM signal loaded with OAM were derived by solving the density matrix equation in the steady state. Then, through coordinate transformation, the spatial distribution construction of the OAM-FWM signal was completed. And the spatial structure of intensity and phase distribution are investigated respectively. It is shown that the Rabi frequency and detuning can effectively control the output OAM-FWM signal. Finally, we further study the phase distribution of multiple topological charge (TC) numbers in the FWM process, considering the conservation of OAM. As a result, the signal can also be regulated by multiple TC numbers. The constructed OAM-FWM signal which has enhanced the information storage capacity, could be widely used in optical communication and quantum information research.
We report on the generation of light carrying orbital angular momentum through Bragg diffraction into an electromagnetically induced coherence grating in a degenerate two-level system of cold cesium atoms. The induced Zeeman coherence grating is shown to contain the spatial phase structure of the incident beams. The exchange of phase information between a light beam with orbital angular momentum and a long-lived atomic coherence opens up the way to process quantum information encoded in a multidimensional state space.
Orbital angular momentum (OAM), characterized by a topological charge ℓ (ℓ integer), serves as a promising vehicle for carrying quantum information. Generating a nonclassical field involving two or more OAM modes can largely enhance the data-carrying capacity of quantum information processing. In this Letter, we present the implementation of a four-wave mixing (FWM) process, featuring a pump beam of a coherent OAM superposition mode and a probe beam of a single OAM mode. We generate twin beams encompassing multiple OAM modes and illustrate their quantum correlation when the pump beam assumes different coherent OAM superposition modes. Furthermore, we analyze the OAM mode components in each output field to deepen our understanding of the nonlinear interaction among different OAM modes. The obtained results show the rich structure of the nonlinear interaction of OAM modes in the FWM process and provide a perspective to study quantum information protocols.
We report on the storage of orbital angular momenta (OAM) of light via the phenomenon of coherent population oscillation (CPO) in cold cesium atoms. The experiment is performed using a delayed four wave mixing configuration, where the transverse optical information of a probe field carrying OAM associated with its azimuthal phase dependence is stored in the CPO of Zeeman sublevels of the hyperfine transition F=3→F'=2 of the cesium D2 line. We also demonstrate experimentally the simultaneous storage and retrieval of different OAM states propagating along different directions in space, leading to algebraic operations with OAM and, therefore, opening the possibility of multiplexing OAM states.