近日，长江大学的杨文星教授课题组取得一项新进展。经过不懈努力，他们成功在双-Λ原子系统中通过反向四波混频实现了光学涡旋相干传输。相关研究成果已于2023年5月19日在国际知名学术期刊《物理评论A》上发表。

该课题组提出并分析了一种在冷原子集合中具有四级双Λ结构的高效方案，实现学光涡旋的相干传输。利用共振反向四波混频（FWM），轨道角动量（OAM）信息可以从入射的涡旋场传输到生成的反向信号场中。在考虑实验可实现的参数以及单个涡旋探测场最初作用于原子集合的一个跃迁的基础上，研究人员确定了共振反向FWM提高光涡旋转换效率的条件，该效率超过了共振正向OAM传输的水平。研究结果表明，光学涡旋的完全能量转换源于线性吸收和参数增益之间的完美竞争。此外，他们还证明了相位失配对于高效传输光学涡旋是不利的。

Title: Coherent transfer of optical vortices via backward four-wave mixing in a double-Λ atomic system

Author: Chun Meng, Tao Shui, Wen-Xing Yang

Issue&Volume: 2023/05/19

Abstract: We propose and analyze an efficient scheme for the coherent transfer of optical vortices in a cold atomic ensemble with four-level double-Λ configuration. The orbital angular-momentum (OAM) information can be transferred from the incident vortex fields to the generated backward signal field via resonant backward four-wave mixing (FWM). Considering the single vortex probe field initially acting on one transition of the atomic ensemble and using experimentally achievable parameters, we identify the conditions under which the resonant backward FWM allows us to greatly improve the conversion efficiency of optical vortices beyond what is achievable in the resonant forward OAM transfers. It is found that the complete energy conversion of optical vortices originates from the perfect competition between linear absorption and parametric gain. We also demonstrate that the phase mismatching would be detrimental to the high-efficiency transfer of optical vortices. Furthermore, we show that the generated backward signal field develops a new pure or mixing OAM state when the control field is also a vortex beam. Finally, we investigate the composite vortex beam generated by collinear superposition of the incident vortex probe and signal fields, which can controlled via adjusting the intensity of the control field. Our scheme may have potential applications in OAM-based optical communication and optical information processing.

DOI: 10.1103/PhysRevA.107.053712

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.107.053712