This research program aims at the experimental study of quantum entanglement in system of single trapped atomic ions and single photons. Entanglement, one of the most striking features of quantum mechanics, leads to strong correlations between the various components of a physical system, regardless of the distance separating them. These correlations were called by Einstein "spooky action at a distance." The entanglement in this project is produced by controlled spontaneous emission of photons by trapped atomic ions; correlated measurement of the photons emitted by two distinct atoms leads to entanglement of these atoms. Since photons can be transmitted over a long distance in optical fibers, the two entangled atoms can be vastly separated. Tests of whether quantum mechanics is required to explain these correlations were designed by physicist John Bell in 1964. The eventual goal of this project is measure the correlations between ions that are approximately 1 km apart in a test of the Bell inequality and providing a means of testing whether "spooky action at a distance" actually occurs, closing a "loophole" in prior experiments. 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 practical quantum repeater system for secure long-distance quantum communications to a somewhat futuristic cluster-state quantum computer. 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. In collaboration with the University of Washington Computer Science and Engineering Department, the hands-on training of information technology industry professionals will be done through their work on the active research projects in the University laboratory.
Quantum computers may help us solve hard computational problems faster than any conventional high-performance computers. These problems include: code breaking, database search, and various simulation problems. Another possible application of these quantum systems is in communications, where quantum cryptography offers the highest possible level of security. New physical systems have to be developed to enable quantum computation. We studied individual atoms of element barium, suspended in vacuum by electromagnetic fields, as a possible candidate for a quantum computer. Techniques for manipulating individual quantum bits ("qubits") were developed. We believe that this system holds promise for quantum computing and long-distance quantum communication. In the course of our investigation we have also measured, to very high precision, some important properties of the atomic structure of barium atomic ions. These measurements may help with the development of the new types of high-precision clocks and future time standards. The higher precision "optical" clocks will enable better GPS and telecommunications, and new technologies beyond our present reach. Further investigation of Ba atomic structure, with even higher precision, may shed new light on the nature of physical world, and lead to discovery of "new physics". Examples of such new physics include: the change of fundamental physical constants with time and (indirect) discovery of new particles.
