Disentanglement of two-qubit system in the Bloch channel

Disentanglement of two qubits is studied in the relaxation process characterized by the longitudinal and transversal relaxation times, T1 and T2, which satisfy the inequality T2 ≤ 2T1 due to the complete positivity of the time-evolution. In the case of sufficiently low temperature, it is shown that whether the equality T2 = 2T1 is satisfied or not is of essential importance in the finite-time disentanglement. This is the characteristic feature of entanglement.