利用线性光学器件,如极化分束器(Polarization beam splitter, PBS), 半波片(Half-wave plate, HWP), 电荷检测器(Charge detector, CD)等的特性以及辅助的单光子可以实现对部分纠缠的两光子系统进行浓缩并得到最大纠缠态。在此基础上,可以直接扩展到N光子的情形。方案中成功的关键部分是当两光子通过第一个极化分束器时,选择它们从不同的输出模射出的情形,此时电荷检测器只包含一个光子。对于两个光子从同一个输出模射出的情形,它可以被利用起来进行下一轮浓缩。迭代浓缩可以获得较高的成功概率。另外该方案中应用的都是线性元件,降低了在实验上实现的难度,具有一定的可行性。

Using the characteristics of the linear optical devices, such as polarization beam splitter(PBS), half-wave plate (HWP) and charge detector(CD), combing with the auxiliary single photon, the partially entangled two-photon system can be concentrated and the maximally entangled state can be obtained. Based on this protocol, it can be directly extended to the case of N-photon system. The pivotal issue of the success of the protocol is selecting the situations where two photons are emitted from different output modes when they pass through the first polarization beam splitter, meanwhile, the charge detector only contains one photon. For the cases where two photons are emitted from the same output mode, it can be used in the next round of entanglement concentration. The repeating concentration can achieve a higher success probability. In addition, the linear components used in this protocol reduce the difficulty in the experiment and have certain feasibility.