Enhancement of Macroscopic Quantum Tunneling by Landau-Zener Transitions

TL;DR

This paper investigates how Landau-Zener transitions can enhance macroscopic quantum tunneling in Josephson junctions with coupled spin-1/2 systems, aligning theoretical predictions with experimental results.

Contribution

It introduces the role of Landau-Zener transitions in increasing tunneling rates in macroscopic quantum systems with spin coupling, providing a new understanding of tunneling enhancement mechanisms.

Findings

Landau-Zener transitions increase tunneling rates.

Qualitative agreement with experimental observations.

Spin flips influence tunneling in imaginary time.

Abstract

Motivated by recent realizations of qubits with a readout by macroscopic quantum tunneling in a Josephson junction, we study the problem of barrier penetration in presence of coupling to a spin-${1\over 2}$ system. It is shown that when the diabatic potentials for fixed spin intersect in the barrier region, Landau- -Zener transitions lead to an enhancement of the tunneling rate. The effect of these spin flips in imaginary time is in qualitative agreement with experimental observations.