Abstract
Coherence lifetimes reflect both the evolution of a quantum system and the conditions under which its state is reconstructed. We study these contributions in Physical--Observation Dual-Axis (PODA) dynamics. For a coherent-state superposition in a passive thermal cavity, we derive the interference envelope and obtain initial-rate lifetimes of $19.73$ and $28.89$ ms from published apparatus parameters. These values agree with the scale of the reported decay, although the envelope lifetime and the time extracted from a tomographic fit need not coincide. The observation coordinate is then allowed to evolve under the same coherent action. Projection onto an isolated cavity mode determines the frequency response and its reciprocal optical force; propagation of the initial covariance gives the relative-phase variance, including the readout reference. For coupled quadratic motion with a classical canonical preparation and a fixed readout reference, a fluctuation--response identity determines the phase-coherence curve from the reciprocal susceptibility and preparation energy. A finite set of stable modes gives recurrent or quasiperiodic coherence. A second relation predicts the ratio of two coherence curves when only the initial observation covariance changes. The common thermal attenuation cancels from this ratio, while the induced physical response remains. Together, these relations connect coherence to response and preparation measurements without introducing a fitted phase-decay rate.