Observation of quantum interference as a function of Berry's phase in a   complex Hadamard optical network
  Emerging models of quantum computation driven by multi-photon quantum interference, while not universal, may offer an exponential advantage over classical computers for certain problems. Implementing these circuits via geometric phase gates could mitigate requirements for error correction to achieve fault tolerance while retaining their relative physical simplicity. We report an experiment in which a geometric phase is embedded in an optical network with no closed-loops, enabling quantum interference between two photons as a function of the phase. 
Anthony Laing, Thomas Lawson, Enrique Mart\'in L\'opez, and Jeremy L.   O'Brien
quant-ph