Coherent Quasiclassical Dynamics of a Persistent Current Qubit

TL;DR

This paper demonstrates a novel regime of coherent qubit dynamics at low frequencies, revealing interference effects and Landau-Zener transitions that persist despite decoherence, supported by a theoretical model.

Contribution

It introduces a new low-frequency regime of coherent qubit dynamics with interference effects, extending understanding beyond high-frequency multiphoton resonances.

Findings

Observation of persistent interference fringes at low driving frequencies

Agreement of the theoretical model with experimental data

Identification of Landau-Zener transitions as a key mechanism

Abstract

A new regime of coherent quantum dynamics of a qubit is realized at low driving frequencies in the strong driving limit. Coherent transitions between qubit states occur via the Landau-Zener process when the system is swept through an energy-level avoided crossing. The quantum interference mediated by repeated transitions gives rise to an oscillatory dependence of the qubit population on the driving field amplitude and flux detuning. These interference fringes, which at high frequencies consist of individual multiphoton resonances, persist even for driving frequencies smaller than the decoherence rate, where individual resonances are no longer distinguishable. A theoretical model that incorporates dephasing agrees well with the observations.