准反事实贝尔态分析

Quasi-Counterfactual Bell-State Analysis

针对被分开在异地的两个纠缠量子比特,本文研究了如何远距离区分纠缠量子比特的四个贝尔态.在区分过程中,利用量子芝诺效应和无相互作用测量,我们可以使任何实际物质粒子出现在两个量子比特之间的公开区域的概率无限趋于零.本文的研究基础是近期被提出的反事实贝尔态分析法[Scientific Reports 8(1),14641,2018].然而,我们发现该方案中的一个重要步骤是不正确的.在本文中,我们对此错误进行了修正.同时,通过使用多重相位操作替代原方案中的多重量子测量,我们还提升了贝尔态分析的成功率.需要指出的是,在反事实贝尔态分析法中,在有限资源的条件下,物质粒子在公开区域中被找到的概率绝对为零,但贝尔态分析的成功率只能无限趋近于1.而在我们的方案中,贝尔态分析的成功率必然为1,而物质粒子在公开区域中被找到的概率不为零,但可以无限趋于零.由于并不能完全杜绝物质粒子出现在公开区域,我们称本方案为准反事实贝尔态分析.两种方案针对不同情况具有不同的优势.

For two entangled qubits separated in different places, this paper studies how to distinguish the four Bell states of the entangled pair remotely. During the process, using quantum Zeno effect and interaction-free measurement, the probability of actual physical particles being found in the open area between the two qubits is nearly zero. The research foundation of this paper is the recently proposed counterfactual Bell-state analysis method [Scientific Reports 8, 14641(2018)]. However, we found that an essential step in the scheme is incorrect. In this paper, we have fixed this error and improved the probability of success of Bell analysis by using multiple phase operations to replace multiple quantum measurements of the original scheme. It should be pointed out that in the counterfactual Bell analysis method, under the condition of limited resources, the probability of physical particles being found in the open area is absolutely zero, but the success rate of Bell analysis can only approach to one. In our scheme, the success rate of Bell-state analysis must be one, and the probability that the physical particles are found in the open area is not zero, but it can tend to zero. Since it is impossible to completely prevent the appearance of physical particles in the open area, we call this scheme quasi-counterfactual Bell-state analysis. The two schemes have different advantages for different situations.