Mixed state entanglement: Manipulating polarization-entangled photons - art. no. 022320

There has recently been much discussion regarding entanglement transformati ons in terms of local filtering operations and whether the optimal entangle ment for an arbitrary two-qubit state could be realized. We introduce an ex perimentally realizable scheme for manipulating the entanglement of an arbi trary state of two polarization-entangled qubits. This scheme is then used to provide some perspective to the mathematical concepts inherent in this f ield with respect to a laboratory environment. Specifically, we look at how to extract enhanced entanglement from systems with a fixed rank, and, in t he case where the rank of the density operator for the state can be reduced , show how the state can be made arbitrarily close to a maximally entangled pure state. In this context we also discuss bounds on entanglement in mixe d states.