Driving forbidden transitions in the fluxonium artificial atom

TL;DR

This paper demonstrates how third-order nonlinear coupling in fluxonium artificial atoms enables driving forbidden transitions, allowing for new quantum control methods at optimal coherence points.

Contribution

It introduces a method to access forbidden transitions in fluxonium atoms using nonlinear coupling, expanding quantum control capabilities.

Findings

Successfully drove forbidden transitions in fluxonium.

Achieved coherent Raman manipulation at sweet spots.

Enabled new quantum operations with protected artificial atoms.

Abstract

Atomic systems display a rich variety of quantum dynamics due to the different possible symmetries obeyed by the atoms. These symmetries result in selection rules that have been essential for the quantum control of atomic systems. Superconducting artificial atoms are mainly governed by parity symmetry. Its corresponding selection rule limits the types of quantum systems that can be built using electromagnetic circuits at their optimal coherence operation points ("sweet spots"). Here, we use third-order nonlinear coupling between the artificial atom and its readout resonator to drive transitions forbidden by the parity selection rule for linear coupling to microwave radiation. A Lambda-type system emerges from these newly accessible transitions, implemented here in the fluxonium artificial atom coupled to its "antenna" resonator. We demonstrate coherent manipulation of the fluxonium artificial atom at its sweet spot by stimulated Raman transitions. This type of transition enables the creation of new quantum operations, such as the control and readout of physically protected artificial atoms.