Sufficient conditions for a disentanglement

Since the introduction of the paradox of Einstein, Podolsky, and Rosen @1# and Schrödinger’s cat @2#, the entanglement of quantum states, i.e., the ability of composite quantum systems to exhibit nonlocal correlations, has been one of the most fascinating consequences of the quantum formalism. Today the entanglement also serves as a basic resource of quantum information theory @3#, which is based upon the idea that the carriers of information are physical objects and as such are subjected to the laws of quantum mechanics. Being of such an importance both for the foundations of quantum mechanics and in the quantum information theory, the phenomenon of entanglement has been extensively studied. Recent studies include characterization and classification of the entanglement, manipulation of the entanglement, and its potential applications @4#. The interplay of the local and global properties of the composite systems is both interesting and important in this context. One of the questions that can be asked is the possibility of erasing the entanglement between the subsystems, while keeping their local properties intact @5#. Two different kinds of the disentanglement procedure were suggested @5#: disentanglement to the product state of the reduced density matrices,