Why do qubit energy-relaxation times fluctuate over hours?
In plain words
The energy-loss time of a given qubit can change several-fold from hour to hour, because defect frequencies wander in and out of resonance with it. Whether interactions between defects fully explain this wandering is not established.
Precise statement
Qubit $T_1$ varies by factors 2-10 over minutes to days, attributed to spectral diffusion of near-resonant two-level defects driven by thermally activated fluctuators with energies $E < T$ (interacting tunneling model; Faoro and Ioffe; Burnett et al. 2014). Test whether the interacting standard tunneling model predicts the spectral-diffusion kernel, the $1/f$ spectrum of defect-frequency noise and its temperature dependence quantitatively, or whether additional mechanisms (quasiparticles, charge traps) are needed.
What would settle it
Long-time defect spectroscopy versus temperature and strain on one device, compared with interacting tunneling-model predictions using independently fixed parameters.