光束分离器算符的分解特性与纠缠功能

Decompositions of beam splitter operator and its entanglement function

光束分离器是量子光学中的基本线性器件之一，它在量子纠缠态的制备与测量上起着重要作用。基于光束分离器（BS）对算符的矩阵变换关系，本文导出了BS算符在若干表象中的自然表示。利用这个自然表示（而非SU（2）李代数关系）及有序算符内的积分技术，可直接导出BS算符的正规乘积、紧指数表示及多种分解形式。此外，可直接导出一种纠缠态表象及其Schmidt分解。这对于讨论连续变量量子隐形传输是十分方便的。

Beam splitter （BS） is a basic linear element in quantum optics, which plays an important role in preparation of entangled states and quantum measurement. On the basis of the transformation relation between operators at input ports and output ports, we derive the natural representations in different representations. Using the natural expression rather than SU（2） Lie algebra relation, as well as the technique of integration within ordered product （IWOP） of operator, we can conveniently and concisely derive the normally ordering form and exponential expression of BS operator. Many forms of decompositions for BS operator can also be directly obtained by its natural representation and the orthogonality of coordinate states. Furthermore, the entangled state representation and corresponding Schmidt decomposition can be conveniently obtained.