Dissipative Landau-Zener transitions of a qubit: bath-specific and universal behavior

TL;DR

This paper investigates Landau-Zener transitions in a qubit coupled to different baths at zero temperature, deriving a universal formula for transition probabilities and analyzing bath-specific effects relevant for quantum technologies.

Contribution

The authors derive a general formula for Landau-Zener transition probabilities in qubits coupled to baths, applicable to various bath types and coupling regimes, highlighting universal and bath-dependent behaviors.

Findings

Diagonal bath coupling yields universal transition probabilities.

Pure off-diagonal coupling makes tunneling sensitive to coupling strength.

Results are relevant for molecular nanomagnets and superconducting qubits.

Abstract

We study Landau-Zener transitions in a qubit coupled to a bath at zero temperature. A general formula is derived that is applicable to models with a non-degenerate ground state. We calculate exact transition probabilities for a qubit coupled to either a bosonic or a spin bath. The nature of the baths and the qubit-bath coupling is reflected in the transition probabilities. For diagonal coupling, when the bath causes energy fluctuations of the diabatic qubit states but no transitions between them, the transition probability coincides with the standard LZ probability of an isolated qubit. This result is universal as it does not depend on the specific type of bath. For pure off-diagonal coupling, by contrast, the tunneling probability is sensitive to the coupling strength. We discuss the relevance of our results for experiments on molecular nanomagnets, in circuit QED, and for the fast-pulse readout of superconducting phase qubits.