Macroscopic Quantum Tunneling of a Fluxon in a Long Josephson Junction

TL;DR

This paper theoretically investigates macroscopic quantum tunneling of a fluxon in a long Josephson junction, considering inhomogeneities and dissipation, and proposes an experimental setup to observe quantum effects.

Contribution

It introduces a theoretical framework for fluxon MQT in inhomogeneous Josephson junctions and proposes an experimental device for observing these quantum phenomena.

Findings

Decay rate estimated using WKB approximation.

Dissipation effects modeled by Caldeira-Leggett theory.

Quantum resonance between two stable states suggests observable MQC.

Abstract

Macroscopic quantum tunneling (MQT) for a single fluxon moving along a long Josephson junction is studied theoretically. To introduce a fluxon-pinning force, we consider inhomogeneities made by modifying thickness of an insulating layer locally. Two different situations are studied: one is the quantum tunneling from a metastable state caused by a single inhomogeneity, and the other is the quantum tunneling in a two-state system made by two inhomogeneities. In the quantum tunneling from a metastable state, the decay rate is estimated within the WKB approximation. Dissipation effects on a fluxon dynamics are taken into account by the Caldeira-Leggett theory. We propose a device to observe quantum tunneling of a fluxon experimentally. Required experimental resolutions to observe MQT of a fluxon seem attainable within the presently available micro-fabrication technique. For the two-state system, we study quantum resonance between two stable states, i.e., macroscopic quantum coherence (MQC). From the estimate for dissipation coefficients due to quasiparticle tunneling, the observation of MQC appears to be possible within the Caldeira-Leggett theory.