Implementation of Pairwise Longitudinal Coupling in a Three-Qubit Superconducting Circuit

Superconducting circuits offer great flexibility in designing quantum hardware. The authors present a multimodal ``trimon'' circuit implementing three qubits, and exploit the strong all-to-all longitudinal coupling to demonstrate high-fidelity multiqubit gates. Their design is a marked departure from conventional ones that combine individual, decoupled qubits. Nonetheless, this scheme allows fairly straightforward scale-up using established multiqubit architectures. The trimon mimics natural molecules, as used in NMR techniques, and shows significant potential for applications in quantum information processing.