利用Sagnac干涉仪实现光子轨道角动量分束器

Realisation of orbital angular momentum sorter of photons based on Sagnac interferometer

光子轨道角动量量子态具有高维和光学涡旋特性,在经典和量子领域展示出了巨大的应用潜力,目前对其的研究已成为物理学的一个热点.本实验研究了利用Sagnac干涉仪干涉的方法将具有不同轨道角动量的光束无破坏地分离到不同的路径,即实现光子轨道角动量分束器.实验中利用此分束器验证了对几种不同轨道角动量态(包含叠加态)的分离,得到了与理论预期相符的实验结果.这种对轨道角动量态的区分的方法相比已有的其他区分方法具有较好的稳定性,而且可用于区分叠加态,也可以达到单光子水平,最重要的是实现了不同的轨道角动量本征态无破坏的与路径比特耦合.这种新方法对高密度通信、量子纠缠、量子保密通信、量子计算与量子信息等方面有着重要的意义.

Orbital angular momentum （OAM） of photons has both classical and quantum applications due to its feature of optical vortex and infinite dimension. OAM discrimination is one of the basic problems, which has been paid much attention recently. Here we present an interferometer method in which a Sagnac interferometer with a Dove prism is placed on each arm to separate the different OAM of photons into different output ports, namely, OAM sorters. We demonstrate experimentally the feasibility of OAM sorter by dividing different OAM states into different output ports. Using the cascade interferometers, we also sort the superposition state successfully. Experimental results are in good agreement with the theoretical predictions. Compared with other methods, this method is more stable and can be used to separate superposition states into single photon levels. Furthermore, this method can also be used to couple OAM modes with spatial modes, a very important method for manipulating OAM states. It is a useful method and has potential applications in high-capacity optical communication, quantum entanglement, quantum cryptography, quantum computation and quantum information.