Multi-mode coupler for high-fidelity two-qubit gate between superconducting qubits

Tunable couplers have become a likely building block for superconducting quantum processors. They have demonstrated high on-off ratio in two-qubit entangling interactions. Qubit-qubit cross-talk can be reduced in the idle mode [1]. Still, the current coupler design is unable to independently control couplings in one- and two-excitation manifolds, which results in unitary errors such as leakage during two-qubit gate operations [2]. We propose a multi-mode tunable coupler design to enable nonlinear couplings in one and two-excitation manifolds, resulting in high on/off coupling ratio in one excitation manifold while maintaining zero coupling in two-excitation manifold [3].