Strategies for discriminating between non-orthogonal quantum states

Any measurement strategy designed to discriminate between nonorthogonal quantum states will have a finite probability of yielding erroneous or inconclusive results. The lower bounds on these probabilities for conclusive and error-free strategies are given by the Helstrom and Ivanovic–Feres limits respectively. We consider intermediate measurements which interpolate between these extremes and derive a general lower bound on the combination of errors and inconclusive results. We also describe a family of measurement strategies which attains this limit.