Distinguishability of maximally entangled states

Abstract

In $2 \otimes 2$, more than 2 orthogonal Bell states with single copy can never be discriminated with certainty if only local operations and classical communication (LOCC) are allowed. More than $d$ orthogonal maximally entangled states in $d \otimed d$, which are in cannonical form, used by Bennett et. al. [Phys. Rev. Lett. 70 (1993) 1895] can never be discriminated with certainty when a single copy of the states is provided. Interestingly we show that all orthogonal maximally entangled states, which are in cannonical form, can be discriminated with certainty if and only if two copies of each of the states are provided. The highly nontrivial problem of local discrimination of $d$ or less no. of pairwise orthogonal maximally entangled states in $d \otimes d$ (in single copy case), which are in cannonical form, is also discussed.