Linear-Optical Implementation of Perfect Discrimination between   Single-bit Unitary Operations
  Discrimination of unitary operations is a fundamental quantum information processing task. Assisted with linear optical elements, we experimentally demonstrate perfect discrimination between single-bit unitary operations using two methods--sequential scheme and parallel scheme. The complexity and resource consumed in these two schemes are analyzed and compared. 
Pei Zhang, Liang Peng, Zhi-Wei Wang, Xi-Feng Ren, Bi-Heng Liu,   Yun-Feng Huang, and Guang-Can Guo