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Single-Atom Quantum Logic Gate and Schrödinger Cat State

C. Monroe, D.M. Meekhof, D. Leibfried, B.E. King, W.M. Itano, and D.J. Wineland, National Institute of Standards and Technology, Boulder, Colo.

One of the fundamental tenets of quantum mechanics is the existence of superposition states, or states whose properties simultaneously possess two or more distinct values. Although quantum superpositions and entanglements seldom appear outside of the microscopic quantum world, there is growing interest in the creation of "big" superpositions and massively entangled states for use in applications such as a quantum computer. We report first steps toward this goal by demonstrating a fundamental two-bit quantum logic gate and a "Schrödinger cat"-like state of motion with a single trapped 9Be+ ion. Both experiments allow sensitive measurements of decoherence mechanisms which will play an important role in the feasibility of quantum computation.