Can a region of space have its own pure quantum state?

In ordinary quantum mechanics, tracing out the rest of the universe leaves a subregion in a mixed state — a fundamental obstacle for defining clean quantum information in gravity. By 'freezing' a spacetime subregion in the gravitational path integral and summing over everything outside, this framework constructs genuinely pure states for subregions. The resulting entropy formula passes nontrivial consistency tests — strong subadditivity, complementarity — and recovers known holographic entropy results as special cases, while hinting that entanglement wedges are observer-dependent.