  Pure dephasing and spontaneous emission are two non-unitary processes of
atoms or spins interacting with fluctuating electromagnetic (EM) modes.
Collective spontaneous emission (e.g., superradiance) originates from
interactions with EM modes in resonance with atoms and has received
considerable attention. Meanwhile, the analogous collective dephasing phenomena
remain poorly understood. Here, we introduce the nano-EM super-dephasing
phenomenon arising in the photonic environment near lossy material interfaces.
We show that this effect is enhanced by over 10 orders of magnitude compared to
free space or photonic cavities due to the presence of long-range correlations
in low-frequency evanescent EM fluctuations. We unravel the universality of
nano-EM super-dephasing behaviors near ferrimagnets, metals, and
superconductors and their dependence on low-frequency material properties. We
demonstrate that the scaling of nano-EM super-dephasing is independent of EM
modes' wavelengths and differs from the conventional $N^2$ scaling of
superradiance by analyzing the decoherence of entangled states, including GHZ
states. Finally, we show how to experimentally isolate and control
super-dephasing to open interesting frontiers for scalable quantum systems.
