Quantum Phase Tomography of a Strongly Driven Qubit

TL;DR

This paper introduces a method called quantum phase tomography that uses Fourier analysis of interference patterns in strongly driven qubits to understand their phase evolution and dephasing mechanisms.

Contribution

It presents a novel approach to visualize and analyze qubit phase dynamics through Fourier transforms of Stueckelberg oscillations, advancing quantum characterization techniques.

Findings

Fourier transforms reveal one-dimensional curves in qubit interference patterns.

Patterns can be used to probe qubit dephasing mechanisms.

Method applicable to various two-level quantum systems.

Abstract

The interference between repeated Landau-Zener transitions in a qubit swept through an avoided level crossing results in Stueckelberg oscillations in qubit magnetization. The resulting oscillatory patterns are a hallmark of the coherent strongly-driven regime in qubits, quantum dots and other two-level systems. The two-dimensional Fourier transforms of these patterns are found to exhibit a family of one-dimensional curves in Fourier space, in agreement with recent observations in a superconducting qubit. We interpret these images in terms of time evolution of the quantum phase of qubit state and show that they can be used to probe dephasing mechanisms in the qubit.