Spectroscopy of mesoscopic Josephson junction using inelastic Cooper-pair tunneling

We have measured the energy levels of a mesoscopic, nearly classical Josephson junction using the method of inelastic Cooper-pair tunneling. The tunneling in an ultrasmall Josephson junction causes transitions in the junction environment and provides a method of doing spectroscopy with a simple DC measurement. A classical Josephson junction can be thought of as an LC-circuit, which quantum mechanically corresponds to the harmonic oscillator. We find that the simple model agrees with the range of EJ/EC ratios down to about 35.