Characterizing and mitigating crosstalk errors of simultaneous entangling gates in a superconducting circuit*

The ability to perform simultaneous two-qubit gates with low error rates is a key requirement to run a quantum algorithm with as short of a circuit depth as possible. However, crosstalk errors in a superconducting qubit system, mostly originating from stray electromagnetic coupling between circuit elements, make it challenging to implement simultaneous entangling gates with high fidelities. Here, we characterize and mitigate crosstalk errors in a 2x2 array of superconducting qubits, where adjacent qubit-qubit interactions are mediated by tunable couplers. We benchmark the fidelities of simultaneous two-qubit gates (CZ-CZ, CZ-iSWAP, or iSWAP-iSWAP) applied on qubit pairs and identify dominant error sources on a case-by-case basis.