Remote Entanglement of Trapped Ions and Loophole-Free Bell Inequality

这个项目的主要目标是研究量子纠缠，这可以说是已经令人困惑的量子力学理论中最令人困惑的特征。量子力学，描述微观世界的理论--基本粒子，原子，分子，光子等等--允许粒子同时出现在许多地方，这种特性称为叠加。如果几个粒子处于叠加态，那么它们的个体属性可能会变得“纠缠”，以至于检测到其中一个粒子会影响其他粒子，即使它们之间没有直接的物理联系。阿尔伯特·爱因斯坦称之为“幽灵般的超距作用”，这种性质没有经典物理学的类比，对它的理解对于验证量子力学的有效性至关重要。这种看似深奥的性质也有重要的实际应用，并对一种快速发展的新技术：量子计算和量子通信产生了影响。量子计算机应该能够使用奇异算法打破计算速度记录;它们的存在需要量子比特或“量子比特”之间的强量子纠缠，这构成了它们运行的基础。量子通信信道可以以最高的安全级别传输数据;这些信道的可靠性和范围关键取决于产生纠缠的能力。PI将使用捕获的Ba离子量子比特和离子-光子纠缠协议来产生离子之间的长距离纠缠。在同一个实验中，需要长距离（~1 km）来关闭局域性漏洞（需要对两个量子比特的测量在彼此的光锥之外）和检测或公平采样漏洞（需要检测效率高）。离子发射的光子将通过光纤发送，并在部分贝尔状态分析仪中进行测量，这一过程反过来又通过纠缠交换使远处的离子纠缠在一起。

The main goal of this project is to study quantum entanglement, which is arguably the most perplexing feature of the already confusing theory of quantum mechanics. Quantum mechanics, the theory that describes the microscopic world--elementary particles, atoms, molecules, photons and so on--allows particles to be at many places at the same time, a property called superposition. If several particles are in a superposition state, then their individual properties may become "entangled" in such a way that detecting one of the particles will affect the other particles even though there is no direct physical connection between them. Dubbed "spooky action at a distance" by Albert Einstein, this property has no classical physics analog, and its understanding is essential for verifying the validity of quantum mechanics. This seemingly esoteric property also has important practical applications and implications for a rapidly developing new technology: quantum computation and quantum communication. Quantum computers should be able to break computational speed records using exotic algorithms; their very existence requires strong quantum entanglement between the quantum bits, or "qubits", which form the basis of their operation. Quantum communication channels can transmit data with the highest possible levels of security; the reliability and range of these channels depends crucially on the ability to generate entanglement.The PI's will use trapped Ba ion qubits and the ion-photon entanglement protocol to generate long distance entanglement between the ions. The long (~1 km) range is needed to close both the locality loophole (which requires the measurements on the two qubits to be outside of each other's light cone) and the detection, or fair sampling, loophole (which requires that the detection efficiency is high) in the same experiment. The photons emitted by the ions will be sent though optical fibers and measured in a partial Bell state analyzer, a process which in turn entangles the distant ions via entanglement swapping.