We present our recent experiments on macroscopic tunneling in the quantum r
egime for underdamped Josephson junctions with different classical-quantum
crossover temperatures. These experiments are performed towards the observa
tion of macroscopic quantum coherence in Josephson systems. A new method to
measure coherence in a two-level system based on the adiabatic inversion i
n an rf squid, is presented This approach could open new perspectives in vi
ew of realization of an elementary quantum bit.