Abstract

Recently it was realized that the CHSH form of Bell's inequalities are not a sufficiently good measure of quantum correlations, in the sense that there are states that do not violate the CHSH inequality, but can be purified by a combination of local interactions and classical communication to yield a state that does violate the CHSH inequality.¹ Therefore, although it is possible to say whether a quantum state is entangled or not,² the amount of entanglement cannot easily be determined for general mixed states. On the basis of quantum optical examples we specify conditions that any measure of entanglement has to satisfy. We then construct a whole class of "good" entanglement measures that are geometrically intuitive.³

© 1997 Optical Society of America