Interacting Qubit-Photon Bound States with Superconducting Circuits

TL;DR

This paper demonstrates experimental control and interaction of qubit-photon bound states in superconducting circuits, enabling tunable, long-range interactions crucial for quantum many-body physics.

Contribution

It reports the first realization of tunable interactions between bound states in a superconducting microwave photonic crystal system.

Findings

Observation of strong coupling via a two-photon virtual process

Tunable on-site and inter-bound state interactions

Potential to create long-range, organized bound state chains

Abstract

Qubits strongly coupled to a photonic crystal give rise to many exotic physical scenarios, beginning with single and multi-excitation qubit-photon dressed bound states comprising induced spatially localized photonic modes, centered around the qubits, and the qubits themselves. The localization of these states changes with qubit detuning from the band-edge, offering an avenue of in situ control of bound state interaction. Here, we present experimental results from a device with two qubits coupled to a superconducting microwave photonic crystal and realize tunable on-site and inter-bound state interactions. We observe a fourth-order two photon virtual process between bound states indicating strong coupling between the photonic crystal and qubits. Due to their localization-dependent interaction, these states offer the ability to create one-dimensional chains of bound states with tunable and potentially long-range interactions that preserve the qubits' spatial organization, a key criterion for realization of certain quantum many-body models. The widely tunable, strong and robust interactions demonstrated with this system are promising benchmarks towards realizing larger, more complex systems of bound states.