多光子多自由度高维光量子计算与量子模拟数据

本数据集名为多光子多自由度高维光量子计算与量子模拟，可以用于开展纠缠源制备、调控和测量的相关研究。数据采集在南京大学固体微结构物理国家重点实验室进行。主要包括双光子双自由度HOM干涉曲线、测量交换相位、完全量子信息掩蔽、6比特量子秘密分享、量子隐形传态、偏振受控非门的保真度、高维轨道角动量pattern及检测等七组实验数据。我们首先对光量子计算的关键资源即超纠缠双光子进行了优化。我们使用超快飞秒激光（脉冲持续时间为150飞秒，重复率为80MHz，中心波长为390纳米）来泵浦I型组合BBO晶体，通过自发参量下转换过程制备双光子对。通过仔细调整泵浦光的空间模式和补偿，制备了高保真度的在偏振和轨道角动量自由度纠缠的超纠缠双光子。利用超纠缠双光子，实验演示了16个处于超纠缠贝尔态的双光子的HOM干涉，通过单光子的幺正变换，我们从SPDC过程产生的一个超纠缠贝尔态出发制备了全部16个超纠缠贝尔态。通过连续调整两光子路径的相对延迟，我们采集得到双光子的HOM干涉曲线。随后我们基于幺正操作技术的双光子干涉实现了对于对称性体系的交换相位的直接测量。我们随后将优化的超纠缠双光子中的偏振纠缠作为掩蔽信道，并利用另外一个可编码的光子的OAM自由度制备超纠缠态，在4量子比特系统中首次实现了完全量子掩蔽。完成掩蔽过程后，又进一步实现了解掩蔽的过程。掩蔽过程和解掩蔽的过程相结合实现了不同量子比特之间的量子隐形传态。作为量子掩蔽协议的重要应用，实现了6量子比特系统中的量子秘密分享，且实验证明了任意初始信息可以被无损地传递给参与秘密分享的任何一方。在掩蔽过程中，偏振自由度的受控非门发挥了关键作用。完全掩蔽的质量好坏主要由偏振受控非门的保真度决定。在数据采集过程中，主要利用780nm波段单光子探测器完成经过相应基矢投影并收集到单模光纤中的自发参量下转换光子对测量。单光子探测器将光信号转换为电信号之后，再利用符合计数器进行符合测量。

This dataset is named Multiphoton, Multidegree-of-Freedom High-Dimensional Optical Quantum Computing and Quantum Simulation. It can be used for research on entanglement source preparation, manipulation and measurement. Data collection was conducted at the National Key Laboratory of Solid State Microstructure Physics, Nanjing University. It mainly includes seven groups of experimental data: Hong-Ou-Mandel (HOM) interference curves of two-photon pairs with two degrees of freedom, measurement of exchange phase, complete quantum information masking, 6-qubit quantum secret sharing, quantum teleportation, fidelity of polarization-controlled NOT (CNOT) gate, high-dimensional orbital angular momentum (OAM) patterns and their detection.

We first optimized the hyper-entangled two-photon pairs, which are the key resources for optical quantum computing. We used an ultrafast femtosecond laser (pulse duration: 150 fs, repetition rate: 80 MHz, central wavelength: 390 nm) to pump a type-I combined BBO crystal, and prepared two-photon pairs via spontaneous parametric down-conversion (SPDC) process. By carefully adjusting the spatial mode of the pump laser and performing compensation, we prepared hyper-entangled two-photon pairs with high fidelity, which are entangled in both polarization and orbital angular momentum (OAM) degrees of freedom.

Using these hyper-entangled two-photon pairs, we experimentally demonstrated HOM interference for 16 two-photon pairs in hyper-entangled Bell states. Through single-photon unitary transformations, we generated all 16 hyper-entangled Bell states starting from one hyper-entangled Bell state produced via the SPDC process. By continuously adjusting the relative delay between the two-photon paths, we collected the HOM interference curves of the two-photon pairs.

Subsequently, we realized direct measurement of the exchange phase for symmetry systems via two-photon interference based on unitary operation techniques. We then took the polarization entanglement from the optimized hyper-entangled two-photon pairs as the masking channel, and used the OAM degree of freedom of another encodable photon to prepare hyper-entangled states, achieving complete quantum information masking for the first time in a 4-qubit system. After completing the masking process, we further implemented the demasking process. The combination of masking and demasking processes realized quantum teleportation between different qubits.

As an important application of the quantum information masking protocol, we realized quantum secret sharing in a 6-qubit system, and experiments verified that any initial information can be transmitted losslessly to any participant in the secret sharing. During the masking process, the polarization-controlled NOT (CNOT) gate played a critical role. The quality of complete quantum information masking is mainly determined by the fidelity of the polarization-controlled NOT (CNOT) gate.

During data collection, 780 nm band single-photon detectors were mainly used to perform measurements of SPDC photon pairs that have been projected onto corresponding bases and collected into single-mode fibers. After converting optical signals into electrical signals by the single-photon detectors, coincidence measurements were performed using a coincidence counter.