Entangled quantum systems meaningfully encode information: A formal demonstration

"Quantum information" refers to the information-theoretic properties of quantum systems. There is still a general prejudice among physicists against the idea that these systems express information due to the nonlocal behavior of entangled quantum systems. The present paper calculates the information content of simple two-state entangled systems (anti-aligned spin-1/2 electron-positron pair, anti-polarized spin-1 photon pair). This calculation involves a modified application of the entropy formalism of quantum statistical mechanics. In addition, the classical and quantum analogues of mutual information are calculated for the entangled particles and experimental devices used to measure them. It is shown that the amount of information expressed by the spin measurement devices depends upon their parameter settings; the spin information of an entangled system prior to measurement is a constant. These results indicate a distinction between information available to a system's sub-components versus that available to measurement devices outside the system. This "inaccessible" information is likely carried by other physical properties of the system.