Frontiers of quantum physics

Abstract:

We investigate spatial entanglement-particle-number entanglement between regions of space-in an ideal bosonic gas. We quantify the amount of spatial entanglement around the transition temperature for condensation (TC) by probing the gas with two localized two-level systems. We show that spatial entanglement in the gas is directly related to filling of the ground-state energy level and therefore to the off-diagonal long-range order of the system and the onset of condensation. © 2007 The American Physical Society.

Abstract:

There has been a great deal of debate surrounding the issue of whether it is possible for a single photon to exhibit nonlocality. A number of schemes have been proposed that claim to demonstrate this effect, but each has been met with significant opposition. The objections hinge largely on the fact that these schemes use unobservable initial states and so, it is claimed, they do not represent experiments that could actually be performed. Here we show how it is possible to overcome these objections by presenting an experimentally feasible scheme that uses realistic initial states. Furthermore, all the techniques required for photons are equally applicable to atoms. It should, therefore, also be possible to use this scheme to verify the nonlocality of a single massive particle.

Abstract:

We investigate entanglement properties of mixtures of short-range spin- s dimer coverings in lattices of arbitrary topology and dimension. We show that in one spatial dimension nearest neighbor entanglement exists for any spin s. Surprisingly, in higher spatial dimensions there is a threshold value of spin s below which the nearest neighbor entanglement disappears. The traditional "classical" limit of large spin value corresponds to the highest nearest neighbor entanglement that we quantify using the negativity. © 2007 The American Physical Society.

Abstract:

We investigate the entanglement properties of resonating-valence-bond states on two and higher dimensional lattices, which play a significant role in our understanding of various many-body systems. We show that these states are genuinely multipartite entangled, while there is only a negligible amount of two-site entanglement. We comment on possible physical implications of our findings.