Bell inequalities and entanglement in solid state devices

Bell inequalities checks constitute a probe of entanglement: for sources of entangled particles, the violation of Bell inequalities is a signature of the non local nature of quantum mechanics. Here, for a solid state device, the inequalities are formulated in terms of current-current cross-correlators, which are natural quantities to consider in mesoscopic physics. The violation of Bell inequalities in a hybrid system where the source is a superconductor thus constitutes a strong indication that the device is a source of entangled electrons (in fact evanescent Cooper pairs), provided that it is connected to appropriate filters.