Heralded linear optical quantum Fredkin gate based on one auxiliary   qubit and one single photon detector
  Linear optical quantum Fredkin gate can be applied to quantum computing and quantum multi-user communication network. In the existing linear optical scheme, two single photon detectors (SPDs) are used to heralding the success of the quantum Fredkin gate while they have no photon count. But analysis results show that for non-perfect SPD the lower the detector efficiency, the higher the heralded success rate by this scheme. We propose an improved linear optical quantum Fredkin gate by designing a new heralding scheme with an auxiliary qubit and only one SPD, in which the higher the detection efficiency of the heralding detector, the higher the success rate of the gate. The new heralding scheme can also work efficiently under non-ideal single photon source. Based on this quantum Fredkin gate, large-scale quantum switching networks can be built. As an example, a quantum Benes network in which only one SPD is used is shown. 
Zhu Chang-Hua, Cao Xin, Quan Dong-Xiao, Pei Chang-Xing
quant-ph