Nanophotonic superdephasing in collective atom-atom interactions

Pure dephasing and spontaneous emission are two nonunitary processes of atoms or spins interacting with fluctuating electromagnetic (EM) modes. The dissipative collective emission processes (e.g., superradiance) originate from interactions with EM modes in resonance with atoms and have received considerable attention. Meanwhile, the analogous nondissipative collective dephasing phenomena mediated by EM environments remain poorly understood. Here, we introduce the nano-EM superdephasing phenomenon arising in the photonic environments near materials. We show that collective dephasing in this nano-EM environment is enhanced by over 10 orders of magnitude compared to free space or cavities. This giant enhancement originates from long-range correlations in off-resonant, low-frequency evanescent EM fluctuations, which lead to collectively accelerated (super) or suppressed (sub) dephasing in many-body entangled states. We further unravel that nano-EM collective dephasing exhibits universal interaction ranges near materials with different anisotropies that can be reciprocal or nonreciprocal. This nano-EM interaction range, which is not present in free space and cavities, leads to unique scaling laws of superdephasing in Greenberger-Horne-Zeilinger states different from the conventional ${N}^{2}$ scaling of superradiance. Finally, we discuss how to experimentally isolate and control superdephasing to open interesting frontiers for scalable quantum systems.