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Measurement of entropy and quantum coherence properties of two type-I entangled photonic qubits
Optical and Quantum Electronics ( IF 3 ) Pub Date : 2021-07-03 , DOI: 10.1007/s11082-021-03067-8
Ali Motazedifard 1, 2, 3 , Seyed Ahmad Madani 1, 2 , N. S. Vayaghan 1, 2
Affiliation  

Using the type-I SPDC process in BBO nonlinear crystal, we generate a polarization-entangled state near to the maximally-entangled Bell-state with high-visibility (high-brightness) 98.50 ± 1.33% (87.71 ± 4.45%) for HV (DA) basis. We calculate the CHSH version of the Bell inequality, as a nonlocal realism test, and find a strong violation from the classical physics or any hidden variable theory, S = 2.71 ± 0.10. Via measuring the coincidence count rate in the SPDC process, we obtain the quantum efficiency of single-photon detectors around (25.5 ± 3.4)%, which is in good agreement to their manufacturer company. As expected, we verify the linear dependency of the CC rate vs. pump power of input CW-laser, which may yield to find the effective second-order susceptibility crystal. Using the theory of the measurement of qubits, includes a tomographic reconstruction of quantum states due to the linear set of 16 polarization-measurement, together with a maximum-likelihood-technique, which is based on the numerical optimization, we calculate the physical non-negative definite density matrices, which implies on the non-separability and entanglement of prepared state. By having the maximum likelihood density operator, we calculate precisely the entanglement measures such as Concurrence, entanglement of formation, tangle, logarithmic negativity, and different entanglement entropies such as linear entropy, Von-Neumann entropy, and Renyi 2-entropy. Finally, this high-brightness and low-rate entangled photons source can be used for short-range quantum measurements in the Lab.



中文翻译:

两种 I 型纠缠光子量子位的熵和量子相干特性的测量

在 BBO 非线性晶体中使用 I 型 SPDC 工艺,我们生成了接近最大纠缠贝尔态的偏振纠缠态,高能见度(高亮度)为 98.50 ± 1.33% (87.71 ± 4.45%) HV ( DA) 基础。我们计算了贝尔不等式的 CHSH 版本,作为非局部现实主义测试,并发现与经典物理学或任何隐藏变量理论S的强烈冲突= 2.71 ± 0.10。通过测量SPDC过程中的符合计数率,我们获得了单光子探测器的量子效率约为(25.5±3.4)%,这与他们的制造商公司非常吻合。正如预期的那样,我们验证了 CC 速率与输入 CW 激光器的泵浦功率的线性相关性,这可能有助于找到有效的二阶磁化率晶体。使用量子位测量理论,包括由于 16 个极化测量的线性集而对量子态进行断层扫描重建,以及基于数值优化的最大似然技术,我们计算物理非负定密度矩阵,这意味着准备状态的不可分离性和纠缠性。通过最大似然密度算子,我们精确计算了纠缠度量,如并发、纠缠、纠缠、对数负性,以及不同的纠缠熵,如线性熵、冯诺依曼熵和仁义 2-熵。最后,这种高亮度低速率纠缠光子源可用于实验室的短程量子测量。

更新日期:2021-07-04
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