An Interaction-Free Quantum Shutter
  We give a proposal for the physical implementation of a quantum shutter. This shutter is a mechanism able to close the passage of light through a slit when present. As it must be a quantum mechanical object, able to show superposition, interesting quantum effects are observed. Finally, we review some applications of the quantum shutter to build quantum memories and a CNOT gate. 
Juan Carlos Garcia-Escartin and Pedro Chamorro-Posada