Resonant enhancement of macroscopic quantum tunneling in Josephson junctions: Influence of coherent two-level systems

M. V. Fistul

doi:10.1103/PhysRevB.92.014505

← Back to search

Resonant enhancement of macroscopic quantum tunneling in Josephson junctions: Influence of coherent two-level systems

M. V. Fistul

DOI 10.1103/PhysRevB.92.014505 · Physical Review B

T1

Active bibliographic source — not scientific approval

Bibliographic access preserves source history; it does not approve extracted materials or validate reported claims. Review warnings on each occurrence separately.

Abstract

We report a theoretical study of the macroscopic quantum tunneling (MQT) in small Josephson junctions containing randomly distributed two-level systems. We focus on a Josephson phase escape for switching from the superconducting (the zero-voltage) state to a resistive one. Above the crossover temperature Tcr the thermal fluctuations of the Josephson phase induce such a switching, and as T<Tcr the regime of the MQT occurs. In the absence of two-level systems (TLSs) a magnetic field applied parallel to the junction plane results in a smooth reduction of Tcr(Φ), where Φ is an applied magnetic flux. As the TLSs are present in Josephson junctions we obtain a resonant enhancement of the MQT. This phenomenon manifests itself by a narrow peak in the dependence of Tcr(Φ) occurring in the intermediate range of Φ, i.e., 0<Φ<ϕ0 (ϕ0 is the magnetic flux quantum). We explain this effect quantitatively by a strong resonant suppression of the potential barrier for the Josephson phase escape that is due to the coherent quantum Rabi oscillations in two-level systems present in the junction.