Abstract The structural dependence of the longitudinal and transversal relaxation times of a two‐level‐system on the transition frequency ω0 and the temperature of the coupled dissipative system has been derived. The fluctuation operators are explicitely given in dependence on the operators and the constants of the dissipative and the two‐level‐system; the corresponding fluctuation correlators have been calculated. If additionally a time‐dependent external force F(t) acts on the system, then the fluctuation correlators depend on the temporal behavior of this force. Due to this effect the run of nonstationary processes which are initiated by quantum noise (e.g., scattering processes) is affected. These considerations have been applied to the case of spontaneous anti‐Stokes Raman scattering with biharmonic vibrational excitation by ultra‐short light pulses. The strength of the external force, which gives rise to an appreciable time dependence of the correlators, has been estimated.
Two-level systems (TLS) are widely recognized as a dominant source of energy relaxation in superconducting qubits, limiting coherence times and device performance. While TLS-induced dissipation is often modeled as independent channels, interacting TLS can form finite many-body environments whose dynamical role in qubit relaxation remains insufficiently understood. Building on the information-erasure-based framework for irreversible thermalization developed in our previous work, we present a microscopic model and numerical simulations of a superconducting qubit coupled to a finite interacting many-body TLS environment as a concrete physical realization of this mechanism. We show that effective irreversible energy relaxation can emerge from intrinsic many-body dynamics without invoking external baths or phenomenological dissipation. The introduction of information erasure drives a transition from coherent oscillatory energy exchange to nonoscillatory exponential relaxation of the qubit. The relaxation times exhibit the scaling
T1,T2∝Jq,τ−2 with respect to the qubit-TLS coupling strength, consistent with Fermi's golden rule and Lindblad-type descriptions. Importantly, both exponential decay and its scaling behavior arise directly from microscopic many-body dynamics. These results provide quantitative insight into TLS-induced decoherence mechanisms and establish a microscopic link between information erasure, many-body thermalization, and irreversible relaxation in superconducting quantum systems.