Free-mode removal and mode decoupling for simulating general superconducting quantum circuits

Superconducting quantum circuits is one of the leading candidates for a universal computer. Designing novel qubit and multiqubit superconducting requires ability to simulate analyze properties general circuit. In particular, going outside transmon approach, we cannot make assumptions on anharmonicity, thus precluding blackbox quantization approaches necessitating formal circuit approach. We consider solve two issues involved in simulating circuits. One handling free modes circuit, that is, with no potential term Hamiltonian. Another issue size, namely challenge strongly coupled multimode The main mathematical tool use address these linear canonical transformation setting mechanics. first by giving provably correct algorithm removing performing completely decouple from other modes. second series different transformations reduce intermode couplings, thereby reducing problem weakly case greatly mitigating overhead classical simulation. benchmark our decoupling methods applying them inductively fluxonium qubits, obtaining several orders magnitude reduction size Hilbert space needs be simulated.