Criss-Crossed Crosstalk: Scalable characterization of crosstalk and spatiotemporally correlated dephasing*

As the size of quantum information processors (QIPs) increases, we need efficient, scalable methods for characterizing noise. In recent years, quantum noise spectroscopy (QNS) protocols have been developed to characterize spatiotemporally correlated noise, but most QNS protocols are limited to single and two-qubit systems. Many of the existing methods for characterizing noise on large QIPs focus on either coherent or Markovian noise. This fails to capture information about temporal correlations in the noise, which can be leveraged to design customized control and error mitigation strategies. To fill this gap, we introduce an extremely scalable protocol for characterizing spatiotemporally correlated dephasing noise as well as long-range ZZ crosstalk in a large, N-qubit QIP. The protocol does not require preparing entangled states or applying two-qubit gates, and the number of measurement settings scales logarithmically with the number of qubits. We demonstrate the effectiveness of our protocol via evaluation on the IBM Quantum Experience.