Let me introduce notation so my question makes sense. A set of orthogonal states can be distinguished by a Q-measurement, e.g. |0> and |1> (Q-computation notation) can be distinguished by measuring with the observable Z which has eigenvectors |0> and |1> with eigenvalues +1 and -1. But if those states represent horizontal and vertically polarized photons then a polarization analyzer (PA(0)) can actually pull off the measurement in the lab. Likewise cosx|0> + sinx|1> and -sinx|0> + cosx|1> can be distinguished by the observable ((cos2x)Z + (sin2x)X)/sqrt2 or using PA(x) on the appropriate polarized photons. The set |00>, |01>, |10>, |11> can be distinguished by using Z or PA(0) on each pair of states or photons. However, what actual PAs or other device lets me distinguish the 4 Bell states (|00> + |11>)/sqrt2, (|00> - |11>)/sqrt2, (|01> +|10>)?sqrt2, and (|01> - |10>)?sqrt2?