Remote Entanglement of Trapped Ions and Loophole-Free Bell Inequality

纠缠是量子力学最奇异的特征之一，它导致量子物体之间的强相关性，而不管它们之间的距离如何。这些相关性被爱因斯坦称为“幽灵般的远距离作用”，对于量子计算和量子通信至关重要。我们通过受控的自发发射的光子捕获的原子离子产生的相关测量的两个远程离子发射的光子导致这些离子的纠缠。由于光子可以在光纤中传输很长的距离，两个纠缠的离子可以相距很远。物理学家约翰·贝尔在著名的“贝尔不等式”中描述了是否需要量子力学来解释这些相关性的测试。该项目的目标是测量两个相距约1公里的离子之间的贝尔不等式。我们将详细研究纠缠和退相干，并进行完全无环洞的贝尔不等式检验，从而加深我们对量子力学的理解，并为量子信息科学发展新的、有用的工具和概念。原子-光子纠缠态的可能应用有很多。它们的范围从用于安全长距离量子通信的量子中继器系统到基于测量的量子计算机技术。该计划的教育部分包括为本科生和研究生提供研究培训，并积极参与前沿研究中物理学代表性不足的群体的学生，开发和建立量子信息科学的本科生和研究生课程，并通过公开讲座和公共活动（如华盛顿大学赫斯基日在西雅图太平洋科学中心）接触更广泛的社会。

Entanglement, one of the most bizarre features of quantum mechanics, leads to strong correlations between quantum objects, regardless of the distance separating them. These correlations, called the "spooky action at a distance" by Einstein, are essential for quantum computing and quantum communications. We produce by controlled spontaneous emission of photons by trapped atomic ions; correlated measurement of the photons emitted by two remote ions leads to entanglement of these ions. Since photons can be transmitted over a long distance in optical fibers, the two entangled ions can be very far apart. Tests of whether quantum mechanics is required to explain these correlations were described by physicist John Bell in the celebrated "Bell inequality". The goal of this project is to measure the Bell inequality between two ions separated by about 1 kilometer. Entanglement and decoherence will be studied in great detail, and a completely loophole-free Bell inequality test will be performed.The research will further our understanding of quantum mechanics, and develop new, useful tools and concepts for quantum information science. Possible applications of the atom-photon entangled state are numerous. They range from a quantum repeater system for secure long-distance quantum communications to the measurement-based quantum computer technology. The educational part of this program includes research training for undergraduate and graduate students and actively involving students from groups underrepresented in physics in cutting edge research, developing and establishing undergraduate and graduate curriculum in quantum information science, and reaching out to the broader society through public lectures and public events, such as the University of Washington Husky Days at the Pacific Science Center in Seattle.