Optimal parameter estimation of depolarizing channel
  We investigate strategies for estimating a depolarizing channel for a finite dimensional system. Our analysis addresses the double optimization problem of selecting the best input probe state and the measurement strategy that minimizes the Bayes cost of a quadratic function. In the qubit case, we derive the Bayes optimal strategy for any finite number of input probe particles when bipartite entanglement can be formed in the probe particles. 
Masahide Sasaki (1 and 2), Masashi Ban (3) and Stephen M. Barnett (4)   ((1)Communications Research Laboratory,(2)CREST, Jap...