Coupling mechanism between microscopic two-level system and superconducting qubits

TL;DR

This paper proposes a numerical scheme to analyze the coupling mechanism between microscopic two-level systems and superconducting flux qubits, revealing flux bias dependence that aids in understanding the coupling nature.

Contribution

It introduces a numerical approach to distinguish coupling mechanisms in flux qubits, overcoming limitations of spectral methods used in phase qubits.

Findings

Coupling strength varies significantly with flux bias in flux qubits.

Spectral methods are insufficient for determining coupling form in phase qubits.

Numerical calculations provide new insights into the coupling mechanism.

Abstract

We propose a scheme to clarify the coupling nature between superconducting Josephson qubits andmicroscopic two-level systems. Although dominant interest in studying two-level systems was in phase qubits previously, we find that the sensitivity of the generally used spectral method in phase qubits is not sufficient to evaluate the exact form of the coupling. On the contrary, our numerical calculation shows that the coupling strength changes remarkably with the flux bias for a flux qubit, providing a useful tool to investigate the coupling mechanism between the two-level systems and qubits.