  An antiferromagnetically exchange-coupled dimer of single molecule magnets
which possesses a large spin tunneling has been investigated. For this system
the ground and first excited states are entangled states and the Hamiltonian is
effectively similar to that of a two-state system at $2s^{\text{th}}$ order in
perturbation theory, thus this system can be mapped to an entangled pseudospin
1/2 particles. We study the effects of interaction and rotation of this system
about its staggered easy-axis direction . The corresponding Hamiltonian of a
rotated two-state entangled spin system is derived with its exact low-energy
eigenstates and eigenvalues. We briefly discuss the effect of a dissipative
environment on this rotated two-state system.
