They say, ``You can't be in two places at one time,'' but ``they'' may be wrong. Scientists at NIST have just disproved the adage by preparing a beryllium atom that is simultaneously located in two widely separated places. Christopher Monroe, Dawn Meekhof, Brian King and David Wineland isolated a single beryllium ion (an atom with one of its two outer electrons stripped away) in an electromagnetic trap and cooled it nearly to absolute zero with precisely tuned laser beams. Next, additional laser pulses were delicately applied, producing tiny forces that gently shoved the ion's two ``superposed'' electron-spin states apart without collapsing them to a single entity. This bizarre state, of being in two well-separated places at once, can be visualized by imagining a large, shallow, round-bottomed bowl with a marble simultaneously at opposite sides of the bowl, rolling from side to side and through itself at the center. The experiment provides a glimpse of quantum superposition states at a scale never seen before. As detailed in the May 24 issue of Science, this experiment has connections to the works of Albert Einstein and Erwin Schroedinger, who described thought experiments in quantum mechanics which seemed to defy reality. Schroedinger, for example, considered the possibility that a cat could be made to be both dead and alive at the same time. ``Schroedinger's cat'' soon became a shorthand way to refer to a whole class of superposed states. Until now, however, no one has ever prepared a particle where the superposition was transformed into a physical separation on so large a scale under such controlled conditions.
