Landau-Zener interferometry with superconducting qubits

TL;DR

This paper demonstrates phase-sensitive Landau-Zener interference in a superconducting qubit, using a Mach-Zehnder interferometer analogy, enabling high-resolution phase and charge detection and novel qubit manipulation techniques.

Contribution

It reports the first observation of quantum interference in Landau-Zener tunneling within a superconducting qubit, introducing a new interferometric approach for quantum control.

Findings

Observation of phase-sensitive interference between Landau-Zener tunneling events.

Implementation of a Mach-Zehnder interferometer analogy in a superconducting qubit.

Potential for high-resolution phase and charge detection using the interferometer.

Abstract

Quantum-mechanical systems having two discrete energy levels are ubiquitous in nature. For crossing energy levels, depending on how fast they approach each other, there is a possibility of a transition between them. This phenomenon is known as Landau-Zener tunneling and it forms the physical basis of the Zener diode, for example. The traditional treatment of the Landau-Zener tunneling, however, ignores quantum-mechanical interference. Here we report an observation of phase-sensitive interference between consecutive Landau-Zener tunneling attempts in an artificial two-level system formed by a Cooper-pair-box qubit. We interpret the experiment in terms of a multi-pass analog to the well-known optical Mach-Zehnder interferometer. In our case, the beam splitting occurs by Landau-Zener tunneling at the charge degeneracy, while the arms of the Mach-Zehnder interferometer in energy space are represented by the ground and excited state. Our Landau-Zener interferometer can be used as a high-resolution detector for phase and charge owing to interferometric sensitivity-enhancement. The findings also demonstrate new methods for qubit manipulations.