Large Dispersive Shift of Cavity Resonance Induced by a Superconducting Flux Qubit in the Straddling Regime

TL;DR

This paper reports a significant enhancement in the dispersive frequency shift of a resonator caused by a superconducting flux qubit in the straddling regime, improving qubit readout contrast.

Contribution

The study demonstrates a large dispersive shift in a coplanar waveguide resonator due to a flux qubit, explained by an extended Jaynes-Cummings model including higher energy levels.

Findings

Achieved an 80 MHz dispersive shift at 5 GHz detuning.

Realized 90% contrast in qubit Rabi oscillations.

Enhanced dispersive shift improves qubit readout fidelity.

Abstract

We demonstrate enhancement of the dispersive frequency shift in a coplanar waveguide resonator induced by a capacitively-coupled superconducting flux qubit in the straddling regime. The magnitude of the observed shift, 80 MHz for the qubit-resonator detuning of 5 GHz, is quantitatively explained by the generalized Jaynes-Cummings model which takes into account the contribution of the qubit higher energy levels. By applying the enhanced dispersive shift to the qubit readout, we achieved 90% contrast of the Rabi oscillations which is mainly limited by the energy relaxation of the qubit.