Noise rectification by a superconducting loop with two weak links
Phys. Rev. B 70 (2004) 024524

A circuit with two Josephson junctions with unequal nonsinusoidal current-phase relation (CPR) can behave as a Brownian motor. As such, it can yield a nonzero average voltage fueled by the equilibrium thermal noise in the junctions.

It was assumed that also the critical currents of the junctions fluctuate. Moreover, it was assumed that, while the critical current Ic(t) wanders in time, the CPR remains fixed, so that for a phase difference ɣ the supercurrent is Ic(t)f(ɣ), where f does not change in time.

In an attempt to find a physical realization of the Josephson junctions invoked by this paper, I considered supercurrent fluctuations in filaments [Phys. Rev. B 80 (2012) 144507]. Disappointingly, the assumption of fixed CPR is not fulfilled. If it were, since f(0)=0, there would be no supercurrent in the absence of a phase difference, despite thermal fluctuations. But there is.