  We have carried out systematic Macroscopic Quantum Tunneling (MQT)
experiments on Nb/Al-AlO_x/Nb Josephson junctions (JJs) of different areas.
Employing on-chip lumped element inductors, we have decoupled the JJs from
their environmental line impedances at the frequencies relevant for MQT. This
allowed us to study the crossover from the thermal to the quantum regime in the
low damping limit. A clear reduction of the crossover temperature with
increasing JJ size is observed and found to be in excellent agreement with
theory. All junctions were realized on the same chip and were thoroughly
characterized before the quantum measurements.
