Entanglement is an essential property of quantum many-body systems. However, its local detection is challenging and was so far limited to spin degrees of freedom in ion chains. Here we measure entanglement between the spins of atoms located on two lattice sites in a one-dimensional Bose-Hubbard chain which features both local spin- and particle-number fluctuations. Starting with an initially lo...

In recent years entanglement has been recognised as a useful resource in quantum information and computation. This applies primarily to pure state entanglement which is, due to interaction with the environment, rarely available. Decoherence provides the main motivation for the study of entanglement distillation. A remarkable effect in the context of distillation is the existence of bound entang...

The quantification of multipartite entanglement is an open and very challenging problem. An exhaustive definition of bipartite entanglement exists and hinges upon the von Neumann entropy and the entanglement of formation, but the problem of defining multipartite entanglement is more difficult and no unique definition exists: different definitions tend indeed to focus on different aspects of the...

We prove that any multiple-copy entanglement transformation fS. Bandyopadhyay, V. Roychowdhury, and U. Sen, Phys. Rev. A 65, 052315 s2002dg can be implemented by a suitable entanglement-assisted local transformation fD. Jonathan and M. B. Plenio, Phys. Rev. Lett. 83, 3566 s1999dg. Furthermore, we show that the combination of multiple-copy entanglement transformation and the entanglement-assiste...

A system of two two-level atoms interacting with a squeezed vacuum field can exhibit stationary entanglement associated with nonclassical two-photon correlations characteristic of the squeezed vacuum field. The amount of entanglement present in the system is quantified by the well known measure of entanglement called concurrence. We find analytical formulas describing the concurrence for two id...

We present entanglement witnesses for detecting genuine multi-qubit entanglement. Our constructions are robust against noise and require only two local measurement settings, independent of the number of qubits. Thus they allow to verify entanglement of many qubits in experiments while requiring only a small effort. In contrast, usual methods need an effort which increases exponentially with the...