QUANTUM CORRELATIONS, LOCAL INTERACTIONS AND ERROR-CORRECTION

We consider the effects of local interactions upon quantum mechanicall y entangled systems. In particular we demonstrate that non-local corre lations cannot il?crease through local operations on any of the subsys tems, but that through the use of quantum error correction methods, co rrelations can be maintained. We provide two mathematical proofs that local general measurements cannot increase correlations, and also deri ve general conditions fur quantum error correcting codes. Using these we show that local quantum error correction can preserve non-local fea tures of entangled quantum systems. We also demonstrate these results by use of specific examples employing correlated optical cavities inte racting locally with resonant atoms. By way of counter example, we als o describe a mechanism by which correlations can be increased, which d emonstrates the need for non-local interactions.