Gómez Santiago, Gómez Esteban S, Jiménez Omar, Delgado Aldo, Walborn Stephen P, Lima Gustavo
Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
Millennium Institute for Research in Optics, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
Sci Rep. 2022 Oct 15;12(1):17312. doi: 10.1038/s41598-022-22314-w.
The problem of non-orthogonal state discrimination underlies crucial quantum information tasks, such as cryptography and computing protocols. Therefore, it is decisive to find optimal scenarios for discrimination among quantum states. We experimentally investigate the strategy for the optimal discrimination of two non-orthogonal states considering a fixed rate of inconclusive outcomes (FRIO). The main advantage of the FRIO strategy is to interpolate between unambiguous and minimum error discrimination by solely adjusting the rate of inconclusive outcomes. We present a versatile experimental scheme that performs the optimal FRIO measurement for any pair of generated non-orthogonal states with arbitrary a priori probabilities and any fixed rate of inconclusive outcomes. Considering different values of the free parameters in the FRIO protocol, we implement it upon qubit states encoded in the polarization mode of single photons generated in the spontaneous parametric down-conversion process. Moreover, we resort to a newfangled double-path Sagnac interferometer to perform a three-outcome non-projective measurement required for the discrimination task, showing excellent agreement with the theoretical prediction. This experiment provides a practical toolbox for a wide range of quantum state discrimination strategies using the FRIO scheme, which can significantly benefit quantum information applications and fundamental studies in quantum theory.
非正交态判别问题是诸如密码学和计算协议等关键量子信息任务的基础。因此，找到量子态之间判别的最优方案具有决定性意义。我们通过实验研究了一种策略，用于在考虑固定不确定结果率（FRIO）的情况下对两个非正交态进行最优判别。FRIO策略的主要优势在于，仅通过调整不确定结果率就能在明确判别和最小错误判别之间进行插值。我们提出了一种通用的实验方案，该方案能对任意一对具有任意先验概率且有任意固定不确定结果率的生成非正交态执行最优FRIO测量。考虑到FRIO协议中自由参数的不同值，我们在由自发参量下转换过程产生的单光子偏振模式编码的量子比特态上实现了该方案。此外，我们采用一种新型的双路径萨格纳克干涉仪来执行判别任务所需的三结果非投影测量，结果与理论预测高度吻合。该实验为使用FRIO方案的广泛量子态判别策略提供了一个实用的工具箱，这能极大地惠及量子信息应用以及量子理论的基础研究。
