Quantum behaviors in high-T_C systems: Macroscopic and vortex quantum tunneling

We describe the main ideas and some experimental outcomes of two experiments, both aimed to study quantum tunneling effects in high-TC structures. In the first experiment, macroscopic quantum tunneling is demonstrated in grain boundary YBaCuO Josephson junctions revealing dissipation levels lower than expected and opening novel perspectives for quantum circuitry. In the second, the low temperature dissipation is dominated by quantum tunneling of individual Pearl vortices in ultra-thin CaBaCuO systems characterized by extremely long Pearl lengths. © 2006 Elsevier B.V. All rights reserved.