See submitted manuscript J. Phys. B. Submitted (2006)
Entanglement is just as coherence considered to be one of the fundamental concepts of quantum mechanics. We did a simple study on the behavior of entanglement between two qubits in the presence of a mutual interaction, a global interaction, decay, and a thermal bath. The result is that regardless of the decay and thermal bath a steady state entanglement is found. The figure shows this. Concurrence which is a quantitative measure for entanglement reaches at large times a non-zero steady state value. The global interaction which is externally controllable can turn the entanglement on and off. We think that this may be interesting for macroscopic systems. If this behavior persists for large systems one can study the macroscopically measurable properties as a function of entanglement.