Bell类检测下的协方差矩阵
Covariance matrices under Bell-like detections
摘要：
我们导出了在一般Bell检测下（n+2）玻色子模式的任意协方差矩阵的变换的简单公式，其中最后两个模式在任意分束器中组合（即，任意transmitted），然后homodyned。特别地，我们考虑了零差探测器非单位量子效率的现实条件。这个公式可以很容易地被专门化来描述标准贝尔测量和外差探测，它们在很多情况下都被利用，包括量子隐形传态协议，纠缠交换和量子密码学。在其一般形式中，我们的公式可以被采用来研究存在实验缺陷和不对称设置的量子信息协议，例如，这是由于使用了不平衡分束器。
英文摘要：
We derive a simple formula for the transformation of an arbitrary covariance matrix of (n+2) bosonic modes under general Bell-like detections, where the last two modes are combined in an arbitrary beam splitter (i.e., with arbitrary transmissivity) and then homodyned. In particular, we consider the realistic condition of non-unit quantum efficiency for the homodyne detectors. This formula can easily be specialized to describe the standard Bell measurement and the heterodyne detection, which are exploited in many contexts, including protocols of quantum teleportation, entanglement swapping and quantum cryptography. In its general form, our formula can be adopted to study quantum information protocols in the presence of experimental imperfections and asymmetric setups, e.g., deriving from the use of unbalanced beam splitters.
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