# Revealing the system-bath coupling via Landau-Zener-St\"uckelberg interferometry in superconducting qubits

## TL;DR

This paper demonstrates how Landau-Zener-Stückelberg interferometry in superconducting flux qubits can be used to identify the nature of environmental noise, revealing differences in interference patterns based on coupling types and time scales.

## Contribution

It introduces a method to distinguish transverse and longitudinal system-bath couplings via analysis of LZS interference patterns in driven superconducting flux qubits.

## Key findings

- N-photon resonances are narrow and symmetric with transverse coupling.
- Longitudinal coupling causes a transition from symmetric to antisymmetric resonance shapes.
- The dynamic behavior aids in interpreting non-stationary LZS experiments.

## Abstract

In this work we propose a way to unveil the type of environmental noise in strongly driven superconducting flux qubits through the analysis of the Landau-Zener-St\"uckelberg (LZS) interferometry. We study both the two-level and the multilevel dynamics of the flux qubit driven by a dc+ac magnetic field. We found that the LZS interference patterns exhibit well defined multiphoton resonances whose shape strongly depend on the time scale and the type of coupling to a quantum bath. For the case of transverse system-bath coupling, the n-photon resonances are narrow and nearly symmetric with respect to the dc magnetic field for almost all time scales, whilst in the case of longitudinal coupling they exhibit a change from a wide symmetric to an antisymmetric shape for times of the order of the relaxation time. We find this dynamic behavior relevant for the interpretation of several LZS interferometry experiments in which the stationary regime is not completely reached.