Motl’s explanation is completely off-base because he’s trying to defend QM from attack when the paper is not trying to attack QM, but trying to distinguish QM from hidden-variables theories.
Of course P(i) = Tr( L | Z(i) >< Z(i) |) … that’s what QM says!
What they’ve just shown is that hidden variables theories that can’t do that, because the ‘real state’ L has specific values, and not a quantum nature.
Motl’s explanation is completely off-base because he’s trying to defend QM from attack when the paper is not trying to attack QM, but trying to distinguish QM from hidden-variables theories.
Of course P(i) = Tr( L | Z(i) >< Z(i) |) … that’s what QM says!
What they’ve just shown is that hidden variables theories that can’t do that, because the ‘real state’ L has specific values, and not a quantum nature.