A Single Atom Transistor in a 1D Optical Lattice
  We propose a scheme utilising a quantum interference phenomenon to switch the transport of atoms in a 1D optical lattice through a site containing an impurity atom. The impurity represents a qubit which in one spin state is transparent to the probe atoms, but in the other acts as a single atom mirror. This allows a single-shot quantum non-demolition measurement of the qubit spin. 
A. Micheli, A. J. Daley, D. Jaksch, and P. Zoller