Measurement of the Intrinsic Subgap Dissipation in Josephson Junctions

We show that the subgap dissipation in sufficiently high-quality Josephson junctions, as measured directly from the current at which the junctions switch from the voltage state into the zero-voltage state, is controlled by thermally excited quasiparticle tunneling. The dissipation is in excellent agreement with a recent theory of Chen, Fisher, and Leggett.