We investigate the potential of future tau neutrino experiments for identifying the ντ appearance in probing secret neutrino interactions, which is very important in a variety of fields, such as neutrino physics, dark matter physics, grand unified theories, astrophysics, and cosmology. The reference experiments include the DUNE far detector utilizing the atmospheric data, which is for the first time probing secret interactions, the Forward Liquid Argon Experiment (FLArE100) detector at the Forward Physics Facility, and emulsion detector experiments such as SND@LHC, FASERν, AdvSND, FASERν2, and SND@SHiP. For concreteness, we consider a reference scenario in which the hidden interactions among the neutrinos are mediated by a single light gauge boson Z′ with a mass at most below the sub-GeV scale and an interaction strength gαβ between the active neutrinos να and νβ. We confirm that these experiments have the capability to significantly enhance the current sensitivities on gαβ for mZ′≲500 MeV due to the production of high-energy neutrinos and excellent ability to detect tau neutrinos. Our analysis highlights the crucial role of “downward-going” DUNE atmospheric data in the search for secret neutrino interactions because of the rejection of backgrounds dominated in the upward-going events. Specifically, ten years of DUNE atmospheric data can provide the best sensitivities on geτ and gμτ which are about 2 orders of magnitude improvement. In addition, the beam-based experiments such as FLArE100 and FASERν2 can improve the current constraint on geτ and gμτ by more than an order of magnitude after the full running of the high luminosity LHC with the integrated luminosity of 3 ab−1. For geμ and gee the SHiP experiment can play the most important role in the high-energy region of mZ′>few 100 MeV, and FLArE100 and FASERν2 can set the most stringent constraints for mZ′ less than few keV, in particular, if atmospheric flux uncertainty reduces DUNE sensitivity. Although our analysis is proceeded under our reference scenario of secret Z′, our analysis strategies can be readily applicable to other types of secret interactions such as Majoron models. Published by the American Physical Society 2024