We measured the intrinsic sub-gap dissipation in a Josephson junction by measuring the currents at which the junctions
retrapped into the zero-voltage state from the voltage state.

"Measurement of the intrinsic sub-gap
dissipation in Josephson junctions",
J.R. Kirtley, C.D. Tesche, W.J. Gallagher, A.W. Kleinsasser, R.L.
Sandstrom, and S.I. Raider, and M.P.A. Fisher,
Phys. Rev. Lett. 61,
2372(1988).