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QI: Fachverband Quanteninformation

QI 14: Quantum Information Poster Session

QI 14.27: Poster

Wednesday, March 11, 2026, 18:00–21:00, P4

Low-overhead Liouvillian Learning of Superconducting Qubit Arrays via Simultaneous Weak Measurements — •Markus Sifft, Armin Ghorbanietemad, and Daniel Hägele — Ruhr University Bochum, Faculty of Physics and Astronomy, Germany

Building on quantum polyspectra for higher-order noise analysis [1,2], we present a low-overhead protocol to reconstruct the Liouvillian of an open system from continuous weak multi-detector measurements of qubits. From a parameterized Liouvillian and measurement operators, we use closed-form expressions for multi-channel polyspectra up to fourth order, which compactly encode coherent dynamics and dissipation. Fitting theory to measured spectra allows us to extract key Hamiltonian and dissipative parameters of superconducting-qubit processors, including qubit frequencies, coherent couplings, crosstalk, drive leakage, and effective temperatures, even with background noise and in the ultra-weak measurement regime. A Fisher-information-based figure of merit quantifies identifiability and optimizes drive frequencies, amplitudes, measurement strengths, and operating temperature. The framework scales to many detectors and qubits, yields error bars and measurement-time estimates, and, compared to standard pulsed characterization, enables spectroscopy-style characterization from a single continuous experiment. All ingredients are implemented in our open-source QuantumCatch [3] and SignalSnap [4] libraries. [1] Hägele, Phys. Rev. B 98, 205143 (2018) [2] M. Sifft et al., arXiv:2505.01231 (2025) [3] github.com/markussifft/quantumcatch [4] github.com/ArminGEtemad/SignalSnap-PyTorch

Keywords: Liouvillian reconstruction; Continuous weak measurement; Quantum polyspectra; Superconducting qubits; Multi-detector noise spectroscopy