Identification and Distance Measures of Measurement Apparatus
  We propose simple schemes that can perfectly identify projective measurement apparatus secretly chosen from a finite set. Entanglements are used in these schemes both to make possible the perfect identification and to improve the efficiency significantly. A brief discussion on the problem of how to appropriately define distance measures of measurements is also provided based on the results of identification. 
Zhengfeng Ji, Yuan Feng, Runyao Duan, Mingsheng Ying