SCHRÖDINGER'S CAT > Implications One important lesson to be learned from Schrödinger's argument is that one should resist the temptation to identify quantum states with the putative properties of a physical system (see also the section on uncertainty). From a technical point of view, quantum states are just vectors that can be used to draw predictions about measurement results obtained in a given experimental context. Hence, in particular, one should not find it disturbing that, in the case of two entangled systems, it turns out to be impossible to assign an individual state to each partner of the pair.

A second important point is that entanglement provides the key tool to understand how a ‘classical world’ can ‘emerge’ within the framework of quantum mechanics. By ‘classical world’ we mean the web of empirical regularities that constitutes our ‘macroscopic experience’. The conceptual framework that we use in ordinary experience proves inadequate to account for quantum phenomena (see wave-particle duality). Nevertheless, as shown in the section about origins, due to the bad isolation of macroscopic systems, quantum mechanics and our common views about cats can coexist without contradiction.

Apart from fundamental implications, the controlled entanglement of atomic and ‘mesoscopic’ systems may lead to dramatic improvements in computer science. In principle, the quantum protocols for processing information are much more effective than those used by usual computers. Indeed, classical bits can only switch between two individual states and they work ‘in series’. Quantum bits, instead can form huge entangled states and thus work ‘in parallel’. Quantum computers are nonetheless exposed to parasitic effects which grow exponentially with dissipation. In order to work, they require perfect isolation from the environment (to an extent that is beyond the reach of current technology).

More generally, the ability to manipulate the quantum state of mesoscopic systems, like biological molecules for example, may lead to new unexpected applications.