Superconducting circuits offer a promising platform for building artificial quantum materials. In 2023, researchers in the EQUS Superconducting Quantum Devices Laboratory – led by Chief Investigator Arkady Fedorov – developed new experimental techniques to create and control exotic quantum states in superconducting waveguide systems.

These systems operate at ultralow temperatures, where quantum effects dominate and superconductivity emerges. The team used superconducting qubits – engineered analogues of atoms – to explore and manipulate a new phase of quantum matter known as an atom–photon bound state. This hybrid quantum state arises when a qubit interacts with the electromagnetic field in a structured waveguide. The bound state is mostly localised on the qubit but also extends as a photon field into the surrounding structure.

By precisely engineering the qubit–waveguide interaction, the researchers demonstrated control over the spatial structure and chirality (directionality) of these bound states – an important step towards using them to engineer more complex quantum systems. Their new scheme enables perfect directional control using just a single tunable qubit, and can be readily implemented in both superconducting and quantum dot platforms.

This work contributes to EQUS Program 1’s goal of engineering strongly interacting, entangled systems with fine-grained control. Atom–photon bound states offer a novel way to couple distant qubits with minimal cross-talk, helping pave the way for scalable, modular quantum architectures. These engineered systems expand the set of quantum behaviours accessible in the lab.

In parallel, the team worked on related technologies with potential applications in quantum computing, clocks, and signal routing. Collaborations across EQUS addressed noise characterisation, quantum-limited measurement, and on-chip signal control –highlighting how precision control over superconducting components can enable the construction of complex, many-body quantum systems from the bottom up.