  Despite being created through a fundamentally quantum-mechanical process,
cosmological structures have not yet revealed any sign of genuine quantum
correlations. Among the obstructions to the direct detection of quantum
signatures in cosmology, environmental-induced decoherence is arguably one of
the most inevitable. Yet, we discover a mechanism of quantum recoherence for
the adiabatic perturbations when they couple to an entropic sector. After a
transient phase of decoherence, a turning point is reached, recoherence
proceeds and adiabatic perturbations exhibit a large amount of self-coherence
at late-time. This result is also understood by means of a non-Markovian master
equation, which reduces to Wilsonian effective-field theory in the unitary
limit. This allows us to critically assess the validity of open-quantum-system
methods in cosmology and to highlight that re(de)coherence from linear
interactions has no flat-space analogue.
