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Physical review. B, Condensed matter

Resonant macroscopic quantum tunneling in small Josephson junctions: Effect of temperature

P. Silvestrini, B. Ruggiero, Yu. N. Ovchinnikov, A. Barone

Published Jan 1, 1996• 11 citations
Publisher

Abstract

Within the well-established quantum picture of Josephson junctions, we study the possibility of resonant macroscopic quantum tunneling. Expressions for the lifetime of metastable states are obtained and the effects of temperature on the main features of the phenomenon are discussed. A "saturation temperature" for the process, below which any temperature effect is negligible, is identified. Quantitative considerations are also given on the actual experimental accessibility to these measurements.

DOI
10.1103/physrevb.53.67

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Within the well-established quantum picture of Josephson junctions, we study the possibility of resonant macroscopic quantum tunneling. Expressions for the lifetime of metastable states are obtained and the effects of temperature on the main features of the phenomenon are discussed. A "saturation temperature" for the process, below which any temperature effect is negligible, is identified. Quantitative considerations are also given on the actual experimental accessibility to these measurements.
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We report a theoretical study of the macroscopic quantum tunneling (MQT) in small Josephson junctions containing randomly distributed two-level systems. We focus on the magnetic field dependent crossover temperature TcrT_{cr}Tcr​ between the thermal fluctuation and quantum regimes of switching from the superconducting (the zero-voltage) state to a resistive one. In the absence of two-levels systems the crossover temperature shows a smooth decrease with an applied magnetic field characterized by an external flux ΦΦΦ. Beyond that we predict a narrow peak in the dependence of Tcr(Φ)T_{cr}(Φ)Tcr​(Φ) occurring in the intermediate range of ΦΦΦ. The effect becomes more pronounced as the junction size increases. We explain this effect quantitatively by a strong resonant suppression of a potential barrier for the Josephson phase escape that is due to the coherent quantum Rabi oscillations in two-level systems present in the junction.
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.
We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular, we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling and thermal activation mechanism. Finally, we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.