Non-perturbative analysis of parametric two-qubit and three-qubit gates

Realizing high fidelity entanglement gates is a major task for near-term quantum hardware. With higher fidelity gates achieved in experiments, more accurate theoretical methods are needed. Here, using non-perturbative formalism, we theoretically study an iSWAP gate activated by frequency modulation in a transmon-transmon pair. We make a comprehensive analysis to directly solve the time-dependency and introduce a continuous set of Fermionic Simulation gates by tuning qubit-qubit detuning and pulse phase. We propose a generalized fast and high fidelity three-qubit-gate that only requires one control pulse, thus eliminating time-misalignment error, which is one of the disadvantages of existing proposals for such gates. Our analysis can serve as an example for studying gates beyond the perturbative regime and RWA.