六光子超纠缠态制备方案

Generation of six-photon hyperentangled states

自发参量下转换对应于一种非线性光学过程,实验上作为一种标准方法,人们利用自发参量下转换源产生纠缠光子对.本文考虑由自发参量下转换源产生三对纠缠光子的情况.通过使用由几组偏振光束分束器、分束器和半波片等线性光学器件组成的量子线路演化三对光子,给出了一个高效制备包含偏振纠缠和空间纠缠的六光子超纠缠态方案.因为方案中包含了参量下转换源产生三对纠缠光子的所有可能情况,所以本方案有很高的效率.基于弱非线性介质构建了一个量子非破坏性测量装置,用于区分光子在两指定的空间模中的两种分布情况.特别地,方案中可以通过合理约束在量子非破坏性测量过程中引入的非线性强度来达到实际实验所限定的数量级,因此,该方案易于在实验上实现.

Nowadays, the nonlinear optical process of spontaneous parametric down-conversion is considered as the canonical approach for creating entangled-photon pairs. We consider three pairs of entangled photons emitted by the parametric down-conversion source, and introduce a setup for evolving these photons based on linear optics, which is composed of several polarizing beam splitters, beam splitters, and half wave plates. By using the parametric down-conversion source and the setup, we carefully design an efficient scheme for preparing six-photon hyperentangled states in both the polarization and the spatial degrees of freedom. Because we use almost all possible behaviors of the three pairs of entangled photons, the present scheme is efficient for creating six-photon hyperentangled states. Next, in the regime of weak nonlinearity we design a quantum nondemolition detection to distinguish the two cases of photons in two special spatial modes. It is worth pointing out that our scheme is much easier to realize, since the strength of the nonlinearities in the process of quantum nondemolition detection can be restricted to the scalable orders of magnitude in practicality.