Quantum versus Classical Information

Berry Groisman, Dan Kenigsberg, Tal Mor

Entanglement is one of the pillars of quantum mechanics and quantum information processing, and as a result the quantumness of nonentangled states has typically been overlooked and unrecognized. We give a robust definition for the classicality versus quantumness of a single multipartite quantum state, a set of states, and a protocol using quantum states. We show a variety of nonentangled (separable) states that exhibit interesting quantum properties, and we explore the ``zoo'' of separable states; several interesting subclasses are defined based on their diagonalizing bases, and their non-classical behavior is investigated.

V. G. Plekhanov

Aharon Brodutch, Berry Groisman, Dan Kenigsberg +1 more

Entanglement is one of the pillars of quantum mechanics and quantum information processing, and as a result, the quantumness of nonentangled states has typically been overlooked and unrecognized until the last decade. We give a robust definition for the classicality versus quantumness of a single multipartite quantum state, a set of states, and a protocol using quantum states. We show a variety of nonentangled (separable) states that exhibit interesting quantum properties, and we explore the “zoo” of separable states; several interesting subclasses are defined based on the diagonalizing bases of the states, and their nonclassical behavior is investigated.

Shunlong Luo, Shuangshuang Fu

The classification and quantification of correlations (classical and quantum) in composite quantum systems are of fundamental significance for quantum information processing. While the paradigm of separability versus entanglement has been intensively studied, the scenario of classicality versus quantumness, with focus on the quantum discord, has also attracted many recent interests. In this paper, pursuing further the latter scenario and exploiting the intrinsic structure of bipartite quantum states via local projective measurements, we introduce the notion of coherent dimension of correlations in terms of the Lüders measurements. The coherent dimension can alternatively be regarded as a generalization of the Schmidt number of a pure state. Furthermore, we propose some families of measures for correlations, which extend naturally both the quantum discord and the quantum mutual information (total correlations), and furthermore interpolate between them. These quantities reveal some hierarchial structures, and provide a more complete description, of both classical and quantum correlations in the quantum realm.