Exactly solvable model for the dynamics of two spin-1/2 particles   embedded in separate spin star environments
  Exact analytical results for the dynamics of two interacting qubits each of which is embedded in its own spin star bath are presented. The time evolution of the concurrence and the purity of the two-qubit system is investigated for finite and infinite numbers of environmental spins. The effect of qubit-qubit interactions on the steady state of the central system is investigated 
Yamen Hamdouni