As transmon based superconducting qubit architectures are one of the most promising candidates for the realization of large-scale quantum computation, it is crucial to know what arethe main sources of the error in the implemented quantum gates. In this work we make a realistic assessment of the contributions of physical error sources to the infidelities of both single and two-qubit gates, where we focus on the non-adiabatic implementation of the CZ gate with tunable couplers. We consider all relevant noise sources, including non-Markovian noise, electronics imperfections and the effect of tunable couplers to the error of the computation. Furthermore, we provide a learning based framework that allows to extract the contribution of each noise source to the infidelity of a series of gates with a small number of experimental measurements.
Tunable coupling of superconducting qubits has been widely studied due to its importance for isolated gate operations in scalable quantum processor architectures. Here, we demonstratea tunable qubit-qubit coupler based on a floating transmon device which allows us to place qubits at least 2 mm apart from each other while maintaining over 50 MHz coupling between the coupler and the qubits. In the introduced tunable-coupler design, both the qubit-qubit and the qubit-coupler couplings are mediated by two waveguides instead of relying on direct capacitive couplings between the components, reducing the impact of the qubit-qubit distance on the couplings. This leaves space for each qubit to have an individual readout resonator and a Purcell filter needed for fast high-fidelity readout. In addition, the large qubit-qubit distance reduces unwanted non-nearest neighbor coupling and allows multiple control lines to cross over the structure with minimal crosstalk. Using the proposed flexible and scalable architecture, we demonstrate a controlled-Z gate with (99.81±0.02)% fidelity.