Two-qubit decoherence mechanisms revealed via quantum process tomography

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 iSWAP 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.