  Characterization of quantum devices generates insights into their sources of
disturbances. State-of-the-art characterization protocols often focus on
incoherent noise and eliminate coherent errors when using Pauli or Clifford
twirling techniques. This approach biases the structure of the effective noise
and adds a circuit and sampling overhead. We motivate the extension of an
incoherent local Pauli noise model to coherent errors and present a practical
characterization protocol for an arbitrary gate layer. We demonstrate our
protocol on a superconducting hardware platform and identify the leading
coherent errors. To verify the characterized noise structure, we mitigate its
coherent and incoherent components using a gate-level coherent noise mitigation
scheme in conjunction with probabilistic error cancellation. The proposed
characterization procedure opens up possibilities for device calibration,
hardware development, and improvement of error mitigation and correction
techniques.
