Witnessing nonseparability of bipartite quantum operations

S Sohail, Ujjwal Sen

Abstract We define a product between quantum superoperators which is preserved under the Choi–Jamiołkowski–Kraus–Sudarshan channel-state isomorphism. We then identify the product as the convolution on the space of superoperators, with respect to which the channel-state duality is also an algebra isomorphism. We find that any witness operator for detecting nonseparability of quantum operations on separated parties can be written entirely within the space of superoperators with the help of the convolution product.

Asher Peres

Jaroslav Řeháček, Z. Hradil

The relative entropy of entanglement of a given bipartite quantum state is calculated by means of a convergent iterative algorithm. When this state turns out to be nonseparable, the algorithm also provides the corresponding optimal entanglement-witness measurement.

Shaurya Bhave

Ming Li, Wang Jing

Marco Barbieri, F. De Martini, G. Di Nepi +3 more

We report on the first experimental realization of an entanglement witness, a method to detect entanglement with few local measurements. The present demonstration has been performed with polarized photons in Werner states, a well-known family of mixed states that can be either separable or nonseparable. The Werner states are generated by a novel high brilliance source of bipartite entangled states by which the state mixedness can be easily adjusted.