Probing non-Markovian qubit noise and modeling Post Markovian Master Equation

Understanding the noise characteristics of quantum processors is crucial when achieving fault-tolerant quantum computing. However, typical qubit designs are often studied under the Markovian approximation, which does not fully capture realistic dynamics. Factors such as qubit-qubit coupling and extended bath correlation times can introduce significant non-Markovian effects into the noise processes. In this study, we employ the Post-Markovian Master Equation (PMME) formalism to characterize memory effects in the noise dynamics. We further experimentally validate the PMME framework using superconducting qubits on an IBM Quantum device, demonstrating clear non-Markovian behavior during circuit execution. Additionally, we quantify the crosstalk effect using an information-theoretic approach and reveal that crosstalk can dominate the observed non-Markovian effects in current quantum hardware.