Extremal quantum correlations: Experimental study with two-qubit states (original) (raw)

We explore experimentally the space of two-qubit quantum correlated mixed states, including frontier ones as defined by the use of quantum discord and von Neumann entropy. Our experimental setup is flexible enough to allow for the high-quality generation of a vast variety of states. We address quantitatively the relation between quantum discord and a recently suggested alternative measure of quantum correlations. PACS numbers: 42.50.Dv,03.67.Bg,42.50.Ex Entanglement, "the characteristic trait of quantum mechanics" according to the words of E. Schrödinger [1], is universally recognized as the key resource in the processing of quantum information and an important tool for the implementation of quantum communication and quantum-empowered metrology . Yet, entanglement does not embody the unique way in which non-classical correlations can be set among the elements of a composite system. When generic mixed states are considered, quantum correlations (QCs) are no longer synonymous of entanglement: Other forms of stronger-thanclassical correlations exist and can indeed be enforced in the state of a multipartite mixed system. However, a general consensus on the measure of quantum correlations is still far from having been found. Among the quantifiers proposed so far, quantum discord [3] (D) occupies a prominent position and enjoys a growing popularity within the community working on quantum information science due to its alleged relevance in the model for deterministic quantum computation with one qubit , extendibility to some important classes of infinitedimensional systems [6] and peculiar role in open-system dynamics . Recently, some attempts at providing an operational interpretation to discord have been reported .