Spectral Threshold Identifies Dissipation Rates in Open Quantum Systems.

Open quantum systems experience energy loss and phase coherence degradation through various dissipative processes, which often produce overlapping dynamic signatures. This study investigates how much information from the Liouvillian spectrum—which summarizes system relaxation—is necessary to accurately distinguish these underlying dissipation rates. Focusing on amplitude damping and dephasing in a six-qubit Lindblad model, the researchers analyzed the slowest non-steady spectral modes. They discovered that population modes provide no information about dephasing, establishing a lower bound on the number of retained modes required for uniform dephasing identifiability. The measured recovery threshold reached this theoretical bound for larger qubit numbers. The study also found that least squares significantly outperformed tabular learning methods in recovering rates from noise-free simulator spectra, though this advantage diminished with spectral perturbations. These results highlight that the quantity and structure of retained spectral information are critical for parameter recovery, independent of the estimator used.