Reduction theorems for optimal unambiguous state discrimination of density matrices
Philippe Raynal, Norbert Lütkenhaus, S. J. van Enk · Physical Review A · 2003
We present reduction theorems for the problem of optimal unambiguous state discrimination of two general density matrices. We show that this problem can be reduced to that of two density matrices that have the same rank n and are described in a Hilbert space of dimensions $2n.$ We also show how to use the reduction theorems to discriminate unambiguously between N mixed states $(N>~2).$