Asymmetric long Josephson junction acting as a ratchet for a quantum field

TL;DR

This paper demonstrates that an asymmetric long Josephson junction can function as a quantum ratchet, rectifying ac currents into dc voltage through quantum field effects, with rectification sign changing near the quantum-classical crossover temperature.

Contribution

It introduces a quantum field theory approach to describe rectification in asymmetric Josephson junctions, revealing temperature-dependent sign reversal of the dc voltage.

Findings

The junction acts as a quantum ratchet under ac drive and magnetic field.

Rectification results from quantum field effects, not particle tunneling.

Rectification sign can reverse near the quantum-classical crossover temperature.

Abstract

We study the escape rate of flux quanta in a long Josephson junction having an asymmetric spatial inhomogeneous critical current density. We show that such a junction can behave as a quantum ratchet when it is driven by an ac current in the presence of a magnetic field. The rectification gives rise to an onset of the dc voltage across the junction. The usual approach of particle-like tunneling cannot describe this rectification, and a quantum field theory description is required. We also show that under definite conditions the rectification direction and, consequently the dc voltage, can change its sign when varying the temperature near the crossover temperature between the quantum and classical regimes.