We study the escape rate of flux quanta in a long Josephson junction having an asymmetric spatial inhomogeneous critical current density. Such a junction can behave as a ratchet when driven by an ac current in the presence of a magnetic field. This rectification gives rise to a dc voltage $V_{\mathrm{dc}}$ across the junction. The usual approach of particlelike tunneling cannot describe this rectification, and a quantum field theory description is required. We also show that, under specific conditions, the rectification direction, and consequently $V_{\mathrm{dc}}$, can change its sign when varying the temperature $T$ near the crossover temperature $T^{*}$ between the quantum and classical regimes.

• Received 10 August 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.190602