Researchers have proposed that spatial subregions in quantum gravity can be described by pure states, rather than the mixed reduced density matrices traditionally employed. This new perspective suggests that the state of a subregion is prepared by a partially "frozen" gravitational path integral, where a spacetime subregion containing the spatial subregion is held fixed, while summing over field configurations and the ambient geometry. This approach represents a significant shift in how entanglement is conceptualized in gravitational systems, seeking a more fundamental description of quantum information in these contexts.

In the semiclassical regime, the proposal includes a holographic prescription for the entanglement entropy of bipartitions of this state. This prescription incorporates a homology constraint analogy adapted to the "frozen" region. The authors state that this formulation satisfies non-trivial self-consistency conditions, such as strong subadditivity, complementarity, and entanglement wedge nesting. Furthermore, it reproduces several known entropy formulas in holography and gravity as special cases, suggesting its robustness and consistency with previous results.

This theoretical construction implies the existence of an observer-dependent "entanglement wedge," labeled by the frozen subregion. This concept could offer new avenues for understanding how quantum information is organized and perceived in a curved spacetime, and how different observers might experience distinct entanglement structures. The proposal opens a path to explore the implications of pure states in quantum gravity, potentially refining our understanding of black holes and the nature of spacetime at fundamental scales.