Quantum random-walk puts single atom into observable superposition of states Answered
Single atoms have been spotted doing the quantum version of the random walk by physicists in Germany. This sighting of a "quantum walk" could help in the design of quantum search algorithms, or in the understanding of the transition from the quantum, microscopic world to the classical, macroscopic world.
Update 15 July 2009: The actual paper appears in this week's Science (pay-per-view, unfortunately). Here's a nice diagram from the article, contrasting (left) the quantum superposition with (right) one of the classicial random walks. The histograms below show their actual measurements in the two situations.