  A major challenge in operating multi-qubit quantum processors is to mitigate
multi-qubit coherent errors. For superconducting circuits, besides crosstalk
originating from imperfect isolation of control lines, dispersive coupling
between qubits is a major source of multi-qubit coherent errors. We benchmark
phase errors in a controlled-phase gate due to dispersive coupling of either of
the qubits involved in the gate to one or more spectator qubits. We measure the
associated gate infidelity using quantum process tomography. In addition, we
point out that, due to coupling of the gate qubits to a non-computational state
during the gate, two-qubit conditional phase errors are enhanced. Our work is
important for understanding limits to the fidelity of two-qubit gates with
finite on/off ratio in multi-qubit settings.
