A Quantum Machine Made of Ions

In computer science, the renowned “extended Church-Turing thesis” says a Turing machine can perform a computation as efficiently as any physical device.  Proof the thesis is wrong would come from showing a quantum machine solves a problem significantly faster than a classical one—and would shake up the current way in which computer scientists classify the difficulty of a problem. In Physical Review Letters, Chao Shen at the University of Michigan, Ann Arbor, and colleagues propose a way to make such a quantum machine with ions.