  The Gibbs free energy properties of a quantum {\it send, receive}
communications system are studied. The communications model resembles the
classical Ising model of spins on a lattice in that the joint state of the
quantum system is the product of sender and receiver states. However, the
system differs from the classical case in that the sender and receiver spin
states are quantum superposition states coupled by a Hamiltonian operator. A
basic understanding of these states is directly relevant to communications
theory and indirectly relevant to computation since the product states form a
basis for entangled states. Highlights of the study include an exact method for
decimation for quantum spins. The main result is that the minimum Gibbs free
energy of the quantum system in the product state is higher (lower capacity)
than a classical system with the same parameter values. The result is both
surprising and not. The channel characteristics of the quantum system in the
product state are markedly inferior to those of the classical Ising system.
Intuitively, it would seem that capacity should suffer as a result. Yet, one
would expect entangled states, built from product states, to have better
correlation properties.
