The fluxonium qubit has emerged as a promising candidate for superconducting quantum computing due to its long coherence times and high-fidelity gates. Nonetheless, further scaling up and improving performance remain critical challenges for establishing fluxoniums as a viable alternative to transmons. A key obstacle lies in developing scalable coupling architectures. In this work, we introduce a scalable fluxonium architecture that enables decoupling of qubit states while maintaining tunable couplings between noncomputational states. Beyond the well-studied $ZZ$ crosstalk, we identify that always-on interactions involving noncomputational levels can significantly degrade the gate fidelities in large systems, thereby impeding scalability. Based on two possible physical realizations of the architecture, we demonstrate that the issue can be mitigated by implementing tunable couplings for fluxonium plasmon transitions, meanwhile enabling fast, high-fidelity gates with passive $ZZ$ suppression. This comparative analysis enables us to establish general principles for realizing the architecture while understanding and addressing implementation-specific challenges.

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• Optoelectronics
• Plasmons
• Quantum computation
• Quantum control
• Quantum gates
• Quantum information with solid state qubits
• Superconducting qubits
• Microwave techniques