Detection of Bell correlations at finite temperature from matter-wave interference fringes

We show that matter-wave interference fringes formed by two overlapping atomic clouds can yield information about the nonlocal Bell correlations. To this end, we consider a simple atomic interferometer, where the clouds are released from the double-well potential and the relative phase is estimated from the density fit to this interference pattern. The Bell correlations can be deduced from the sensitivity of the phase obtained in this way. We examine the relation between these two quantities for a wide range of ground states of the double-well, scanning through the attractive and the repulsive interactions. The presented analysis includes the effects of finite temperature, when excited states are thermally occupied. We also consider the impact of the spatial resolution of the single-atom detectors, the fluctuations of the energy mismatch between the wells, and the atom-number fluctuations. These results establish a link between the fundamental (nonlocality) and the application-oriented (quantum metrology) aspects of entanglement.