Noise-Tolerant Superconducting Gates with High Fidelity

We design two-qubit quantum gates by coupling two Transmon qubits with a capacitor and study the time-dependent dynamics of the qubit–qubit interaction for different inter-qubit interaction strengths in the presence of quantum noise. Particularly, we focus on three famous quantum gates, iSWAP, bSWAP, and CNOT. In this study, we investigate different types of noises, such as emission, absorption, and dephasing. Two-qubit gates, iSWAP and bSWAP, are modeled by direct variable coupling between two Transmon qubits. In addition, we construct the CNOT gate, using three qubits, where the two qubits are used for inputs and outputs, and the middle qubit acts as a tunable coupler between the two qubits. The middle qubit is needed for energy conservation; we called it a garbage bit, since we do not use it in logical operations. For the two input/output coupled qubits, direct variable capacitor coupling is also used. In view of the coupled Lindblad master equations, we study the time-dependent dynamics of our proposed quantum models. A significant impact of emission/absorption quantum noise can be seen on iSWAP, bSWAP, and CNOT gates, as compared to dephasing noise. Additionally, we also discuss the generation of entanglement for different scenarios with and without noises.