  There is a wide recognition that Josephson-junction-like structures intrinsic
to the layered cuprate high temperature superconductors offer an attractive
stage for exploiting possible applications to new quantum technologies. On the
other hand the low energy quasiparticle excitations characteristically present
in these d-wave superconductors may easily destruct the coherence required.
Here we demonstrate for the first time the feasibility of macroscopic quantum
tunneling in the intrinsic Josephson junctions of a high temperature
superconductor, and find it to be characterized by a high classic-to-quantum
crossover temperature and a relatively weak quasiparticle dissipation.
