Minimum-error state discrimination and Fano's inequality

The discrimination between non-orthogonal quantum states plays a pivotal role in quantum information processing and quantum technology. Strategies that minimize the error probability are of particular importance, but they are only known for special classes of problems. Certain forms of Fano's inequality yield a bound on the error probability, but it is not known how close this bound is to the minimum-error probability achieved by means of optimal measurements. In this work, we discuss how the minimum-error probability compares to the error bound obtained through the Fano's inequality for several scenarios, some of which are amenable to analytic treatments.