Extracting Classical Correlations from a Bipartite Quantum System

In this paper we discuss the problem of splitting the total correlations for a bipartite quantum state described by the Von Neumann mutual information into classical and quantum parts. We propose a measure of the classical correlations as the difference between the Von Neumann mutual information and the relative entropy of entanglement. We compare this measure with different measures proposed in the literature.Comment: 5 pages, 1 figur

Remote information concentration using a bound entangled state

Remote information concentration, the reverse process of quantum telecloning, is presented. In this scheme, quantum information originally from a single qubit, but now distributed into three spatially separated qubits, is remotely concentrated back to a single qubit via an initially shared entangled state without performing any global operations. This entangled state is an unlockable bound entangled state and we analyze its properties.Comment: 4 pages, 2 figure

Teleportation as a Depolarizing Quantum Channel, Relative Entropy and Classical Capacity

We show that standard teleportation with an arbitrary mixed state resource is equivalent to a generalized depolarizing channel with probabilities given by the maximally entangled components of the resource. This enables the usage of any quantum channel as a generalized depolarizing channel without additional twirling operations. It also provides a nontrivial upper bound on the entanglement of a class of mixed states. Our result allows a consistent and statistically motivated quantification of teleportation success in terms of the relative entropy and this quantification can be related to a classical capacity.Comment: Version published in Phys. Rev. Let

Quantum superposition of multiple clones and the novel cloning machine

we envisage a novel quantum cloning machine, which takes an input state and produces an output state whose success branch can exist in a linear superposition of multiple copies of the input state and the failure branch exist in a superposition of composite state independent of the input state. We prove that unknown non-orthogonal states chosen from a set $\cal S$ can evolve into a linear superposition of multiple clones by a unitary process if and only if the states are linearly independent. We derive a bound on the success probability of the novel cloning machine. We argue that the deterministic and probabilistic clonings are special cases of our novel cloning machine.Comment: Two column, 5 pages, Latex, some additions, minor changes. Phys. Rev. Lett. (To appear, 1999

Entangled Rings

Consider a ring of N qubits in a translationally invariant quantum state. We ask to what extent each pair of nearest neighbors can be entangled. Under certain assumptions about the form of the state, we find a formula for the maximum possible nearest-neighbor entanglement. We then compare this maximum with the entanglement achieved by the ground state of an antiferromagnetic ring consisting of an even number of spin-1/2 particles. We find that, though the antiferromagnetic ground state does not maximize the nearest-neighbor entanglement relative to all other states, it does so relative to other states having zero z-component of spin.Comment: 19 pages, no figures; v2 includes new results; v3 corrects a numerical error for the case N=