论文标题
矢量涡流梁是否赋予任何纠缠？
Are vector vortex beams endowed with any entanglement?
论文作者
论文摘要
光束极化是最重要的物理现象之一。但是到目前为止，仅在近后近似中描述了它被认为是单个自由度，其特征在横向平面上以局部stokes参数为特征。基于这样的描述，矢量涡流梁被认为是在极化和空间模式下纠缠的。在这里，我们表明，在包括众所周知的圆柱矢量梁在内的大量代表性矢量涡流梁中没有任何纠缠。这是通过开发一种准确表征一般光束极化的方法来实现的。发现在动量空间中严格地对一般光束进行概括性时，这些参数是相对于自然坐标系的物理量。所谓的stratton矢量确定自然坐标系为极化的自然表示，其中保利矩阵代表了相对于自然坐标系统的固有自由度。结果，斯特拉顿矢量本身是两极分化的另一种自由度。从这个角度来看，由平行于传播轴的stratton矢量以及Pauli矩阵$ \hatσ_1$的特征值所指定的光束是矢量涡流梁。他们没有任何纠缠。
Polarization of light beams is one of the most important physical phenomena. But up till now it was only described in the paraxial approximation in which it is considered to be a single degree of freedom that is characterized by the local Stokes parameters over the transverse plane. Based on such a description, vector vortex beams are considered to be entangled in polarization and spatial mode. Here we show that there is not any entanglement in a large class of representative vector vortex beams, including the well-known cylindrical-vector beams. This is achieved by developing an approach to exactly characterize the polarization of a general beam. It is found that the Stokes parameters, when generalized rigorously to a general beam in momentum space, are physical quantities with respect to a natural coordinate system. The so-called Stratton vector determining the natural coordinate system fixes a natural representation for the polarization in which the Pauli matrices represent the intrinsic degree of freedom of the polarization with respect to the natural coordinate system. As a result, the Stratton vector itself shows up as another degree of freedom of the polarization. From this point of view, the light beams specified by a Stratton vector parallel to the propagation axis as well as by the eigenvalues of the Pauli matrix $\hatσ_1$ are precisely vector vortex beams. They are not endowed with any entanglement.
