Adaptive schemes for incomplete quantum process tomography
  We propose an iterative algorithm for incomplete quantum process tomography, with the help of quantum state estimation, based on the combined principles of maximum-likelihood and maximum-entropy. The algorithm yields a unique estimator for an unknown quantum process when one has less than a complete set of linearly independent measurement data to specify the quantum process uniquely. We apply this iterative algorithm adaptively in various situations and so optimize the amount of resources required to estimate the quantum process with incomplete data. 
Yong Siah Teo, Berthold-Georg Englert, Jaroslav Rehacek, and Zdenek   Hradil
quant-ph