  In the task of discriminating between nonorthogonal quantum states from
multiple copies, the key parameters are the error probability and the resources
(number of copies) used. Previous studies have considered the task of
minimizing the average error probability for fixed resources. Here we introduce
a new state discrimination task: minimizing the average resources for a fixed
admissible error probability. We show that this new task is not performed
optimally by previously known strategies, and derive and experimentally test a
detection scheme that performs better.
