Characterization of a noisy quantum process by complementary classical   operations
  One of the challenges in quantum information is the demonstration of quantum coherence in the operations of experimental devices. While full quantum process tomography can do the job, it is both cumbersome and unintuitive. In this presentation, we show that a surprisingly detailed and intuitively accessible characterization of errors is possible by measuring the error statistics of only two complementary classical operations of a quantum gate. 
Holger F. Hofmann, Ryo Okamoto and Shigeki Takeuchi