We analyze the quantum process tomography (QPT) in the presence of decoherence, focusing on distinguishing local and nonlocal decoherence mechanisms for a two-partite system from experimental QPT data. In particular, we consider the $\sqrt{i\text{SWAP}}$ gate realized with superconducting phase qubits and calculate the QPT matrix $\chi$ in the presence of several local and nonlocal decoherence processes. We determine specific patterns of these decoherence processes, which can be used for a fast identification of the main decoherence mechanisms from an experimental $\chi$ matrix.

• Received 30 March 2009

DOI:https://doi.org/10.1103/PhysRevA.80.042103