  We define threshold disentanglement (TD) as the level above which
entanglement must be maintained for later use and calculate the values of
quantum system parameters at $t=0$ that will ensure that the threshold is not
crossed in a specified time. An important issue is the possibility of
non-smooth, typically non-exponential, decay of entanglement into the state of
complete disentanglement (CD). Given a specified operation time $\tau$, we
determine phase diagrams showing entanglement preservation during the evolution
of a generic two-qubit mixed state as a function of selected initial parameters
such as concurrence and excitation probabilities. In other words,
disentanglement can be pre-managed through these parameters. Three common
relaxation processes - amplitude, phase and depolarization - are considered.

Quantum Physics