Parametric Coupling of Three Transmons for Multi-Qubit Interactions

Superconducting qubit architectures have largely converged on pairwise nearest-neighbor coupling mediated by capacitive couplers. While effective for scalable layouts, such localized connectivity introduces circuit decomposition overhead, requiring numerous SWAP operations and limiting the available entangling operations to two-qubit gates. Multi-qubit (N > 2) gates, by contrast, are useful resources for quantum algorithms, simulation, and error correction.

We present experimental progress on a system of three superconducting transmon qubits galvanically coupled through a common tunable SQUID element. This architecture enables all-to-all connectivity with high on/off coupling ratios, supporting fast, parametrically driven two- and three-qubit gates as well as tunable dispersive interactions that can suppress residual pairwise ZZ couplings. We will report recent experimental results demonstrating these capabilities.