The Berkeley experiments used a biased junction
In 1984–1985, Clarke, Devoret and Martinis studied a carefully isolated Josephson circuit. Bias created metastable states for a collective phase coordinate. Leaving one of those states produced an electrical switching signal that could be counted repeatedly.
The 2025 award recognized macroscopic quantum tunneling and energy quantization in a circuit. The physical claim concerns a collective electrical degree of freedom, not the literal passage of the whole apparatus through a wall.
Temperature dependence tested escape mechanisms
At higher temperature, thermal activation can lift the phase over the potential barrier. At sufficiently low temperature, tunneling can dominate. Distinguishing them required a known circuit potential, temperature control and careful treatment of the electromagnetic environment.
Sources: [1]
Microwave resonances tested discrete levels
Microwaves changed the escape probability at selected frequencies, consistent with transitions between discrete metastable levels. That frequency structure supplied evidence different from a low-temperature escape plateau. Resonance positions and rates had to agree with the same circuit parameters.
The new and existing Labs keep those questions separate
The switching Lab studies biased escape statistics in separate limiting rate approximations. The existing Transmon Lab studies a different circuit spectrum; the SQUID Lab studies flux interference. Together they explain related Josephson physics; each keeps its own geometry, while this article traces the evidence from the historical biased junction.