Stark effect and generalized Bloch-Siegert shift in a strongly driven two-level system

TL;DR

This paper investigates the Stark effect and Bloch-Siegert shift in a strongly driven superconducting qubit, revealing significant shifts that require advanced theoretical models for accurate explanation.

Contribution

It demonstrates the observation of pronounced Stark shifts in a superconducting qubit under ultrastrong driving, extending understanding beyond the lowest-order Bloch-Siegert correction.

Findings

Observed large Stark shifts in a superconducting qubit

Measured quasienergies consistent with Floquet theory

Identified need for higher-order corrections beyond Bloch-Siegert

Abstract

A superconducting qubit was driven in an ultrastrong fashion by an oscillatory microwave field, which was created by coupling via the nonlinear Josephson energy. The observed Stark shifts of the `atomic' levels are so pronounced that corrections even beyond the lowest-order Bloch-Siegert shift are needed to properly explain the measurements. The quasienergies of the dressed two-level system were probed by resonant absorption via a cavity, and the results are in agreement with a calculation based on the Floquet approach.