Fast two-qubit gates between inductively-capacitively coupled fluxoniums

Among various superconducting qubits, fluxonium qubit has the advantage of longer than 1ms coherence time and large nonlinearity. However, to build a quantum processor, one problem in scaling up the qubits is the residual ZZ-coupling between connected qubits, which introduces unwanted crosstalk between qubits and prevents local operation. Introducing a tunable coupler is one approach to suppressing the ZZ coupling to the sub-MHz values. We present an alternative approach when the ZZ interaction is reduced to a kHz range thanks to direct capacitive and inductive interactions between a pair of fluxoniums. We analyze the interplay between these two interactions that reduce unwanted ZZ couplings. We then analyze several other fluxonium gate schemes, such as microwave-activated CZ, cross-resonance CNOT, and SWAP gates. We find optimal parameters for these gates to achieve high fidelity.