Observation of macroscopic Landau-Zener transitions in a superconducting device

TL;DR

This paper reports the observation of macroscopic Landau-Zener transitions in a superconducting qubit, demonstrating quantum coherence effects in a macroscopic quantum device.

Contribution

First experimental observation of Landau-Zener transitions in a superconducting qubit coupled to a resonant circuit, highlighting quantum coherence at a macroscopic scale.

Findings

Landau-Zener transitions observed in a superconducting device

Quantum coherence demonstrated in a macroscopic quantum system

Coupling between qubit and resonant circuit characterized

Abstract

A two-level system traversing a level anticrossing has a small probability to make a so-called Landau-Zener (LZ) transition between its energy bands, in deviation from simple adiabatic evolution. This effect takes on renewed relevance due to the observation of quantum coherence in superconducting qubits (macroscopic "Schrodinger cat" devices). We report an observation of LZ transitions in an Al three-junction qubit coupled to a Nb resonant tank circuit.