Rabi spectroscopy of a strongly driven qubit-fluctuator system

TL;DR

This paper investigates the complex dynamics of a superconducting phase qubit strongly coupled to a microscopic two-level fluctuator, revealing asymmetries in Rabi oscillations caused by higher-level interactions.

Contribution

It demonstrates how higher qubit levels induce effective coupling to the TLF, leading to observable asymmetries in Rabi spectroscopy, advancing understanding of qubit-fluctuator interactions.

Findings

Observation of asymmetric Rabi oscillations near TLF resonance

Identification of higher-level effects causing asymmetry

Experimental validation of theoretical model

Abstract

Superconducting qubits often show signatures of coherent coupling to microscopic two-level fluctuators (TLFs), which manifest themselves as avoided level crossings in spectroscopic data. In this work we study a phase qubit, in which we induce Rabi oscillations by resonant microwave driving. When the qubit is tuned close to the resonance with an individual TLF and the Rabi driving is strong enough (Rabi frequency of order of the qubit-TLF coupling), interesting 4-level dynamics are observed. The experimental data shows a clear asymmetry between biasing the qubit above or below the fluctuator's level-splitting. Theoretical analysis indicates that this asymmetry is due to an effective coupling of the TLF to the external microwave field induced by the higher qubit levels.