Rabi oscillations of a qubit coupled to a two-level system

TL;DR

This paper investigates how a qubit's Rabi oscillations are affected by coupling to a two-level fluctuator and a heat bath, revealing significant suppression near resonance and implications for experimental read-out signals.

Contribution

It develops a phenomenological scheme to incorporate phase and energy relaxation while fully modeling the quantum dynamics of a driven four-level system.

Findings

Rabi oscillations are significantly suppressed near resonance.

The fluctuator state notably alters the read-out signal.

The results are relevant to recent experimental observations.

Abstract

The problem of Rabi oscillations in a qubit coupled to a fluctuator and in contact with a heath bath is considered. A scheme is developed for taking into account both phase and energy relaxation in a phenomenological way, while taking full account of the quantum dynamics of the four-level system subject to a driving AC field. Significant suppression of the Rabi oscillations is found when the qubit and fluctuator are close to resonance. The effect of the fluctuator state on the read-out signal is discussed. This effect is shown to modify the observed signal significantly. This may be relevant to recent experiments by Simmonds et al. [Phys. Rev. Lett. 93, 077003 (2004)].