Mesoscopic Systems

Our research focuses on the design and functionality of mesoscopic solid state devices, their transport and noise properties, and their potential use in quantum information theory. We have suggested specific mesoscopic structures allowing for the study of basic quantum phenomena such as entanglement and wave function collapse. We have shown how to test for the non-classical correlations through the use of a Bell inequality test based on current-current cross correlators. We have suggested a design for a solid-state entangler using a normal-metal--superconductor junction injecting entangled pairs of quasi-particles into a normal-metal lead. Here, the quantum correlated two-particle states arise from Cooper pairs decaying into the normal lead and are characterized by entangled spin- and orbital degrees of freedom. In an alternative setup with a normal-metal device in a fork geometry the entanglement is produced via postselection in the measurement process (non-interacting limit). Both, the dc and pulsed production of entangled pairs has been analyzed. In our recent work we have unveiled the relation between the fidelity (stability under perturbation) of a quantum system and the generating function of full counting statistics and have analyzed the possibility of their measurement using a quantum bit as a measurement device.