Experimental verification of fault tolerant quantum key distribution protocol.

We have investigated fault tolerant quantum key distribution experimentally, using four polarization encoding two-qubit states generated by spontaneous parametric down conversion. Collective noises on polarization and phase were simulated by passing the states through a half wave plate and a quarter wave pate. Error rate was calculated by measuring the two-qubit states in three basis. Our results show that the protocol is tolerant under collective random unitary noise.