Experimental demonstration of a non-destructive controlled-NOT quantum   gate for two independent photon-qubits
  Universal logic gates for two quantum bits (qubits) form an essential ingredient of quantum information processing. However, the photons, one of the best candidates for qubits, suffer from the lack of strong nonlinear coupling required for quantum logic operations. Here we show how this drawback can be overcome by reporting a proof-of-principle experimental demonstration of a non-destructive controlled-NOT (CNOT) gate for two independent photons using only linear optical elements in conjunction with single-photon sources and conditional dynamics. Moreover, we have exploited the CNOT gate to discriminate all the four Bell-states in a teleportation experiment. 
Zhi Zhao, An-Ning Zhang, Yu-Ao Chen, Han Zhang, Jiangfeng Du, Tao   Yang, Jian-Wei Pan