Quantumness versus entanglement in quantum measurements

Gerardo Adesso, Marco Piani

Philip Bechtle, Cedric Breuning, Herbi K. Dreiner +1 more

It has been argued more than 30 years ago that it is not possible to test locality at colliders, due to the inability to directly measure non-commutating observables such as spin components in current collider experiments. Recently, there has been a lot of phenomenological and experimental activity around testing locality via Bell-type experiments or entanglement versus non-entanglement in a collider environment. These results seem to evade the earlier no-go theorem by indirectly measuring spin correlations via their relation to angular correlations between momenta. We perform a careful study of the feasibility of such an approach. We scrutinize the relationship between spin and angular correlations in both quantum mechanics and local hidden variable theories. Our conclusion is that it is currently not possible to perform a logically coherent set of experimental measurements at colliders that would allow one to test locality or entanglement versus non-entanglement. This reaffirms the earlier no-go theorem. We stress that the no-go theorem does not apply to measurements of observables inspired from entanglement and Quantum Information Theory to test the Standard Model of particle physics.

Leah Henderson

C. W. J. Beenakker

I. Introduction (Preface, Exciton entanglers, Photon entanglers) II. Entanglement basics (Quantum versus classical correlations, Bell inequality, Entanglement measures for pure states, Entanglement measures for mixed states, Particle conservation, Phase reference) III. How to entangle free particles (Free bosons, Free fermions) IV. Spin versus orbital entanglement V. Entanglement detection by noise measurements (Tunneling regime, Beyond the tunneling regime, Full counting statistics) VI. Loss of entanglement by dephasing VII. Quantum entanglement pump VIII. Teleportation by electron-hole annihilation IX. Three-qubit entanglement X. The experimental challenge

Sreetama Das, Titas Chanda, Maciej Lewenstein +3 more

We present a review of the problem of finding out whether a quantum state of two or more parties is entangled or separable. After a formal definition of entangled states, we present a few criteria for identifying entangled states and introduce some entanglement measures. We also provide a classification of entangled states with respect to their usefulness in quantum dense coding, and present some aspects of multipartite entanglement.