Remote Entanglement of Trapped Ions and Loophole-Free Bell Inequality

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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.