Dephasing Rate in Dielectric Glasses at Ultralow Temperatures

A novel mechanism for dephasing in dielectric glasses is considered. The mechanism is due to the delocalized collective excitations arising in the ensemble of the interacting two-level systems. The spectral diffusion induced by these excitations gives rise to the phonon-independent transverse relaxation. The mechanism results in the linear temperature dependence of the dephasing rate and becomes predominant at ultralow temperatures. A qualitative agreement with the experimental data is found.