I think you're suggesting something along the lines of using entanglement of superposition to indicate observation (as in a MITM attack) by collapsing, but that

I think you're suggesting something along the lines of using entanglement of superposition to indicate observation (as in a MITM attack) by collapsing, but that's really hard (like, on a physical level) to maintain over useful distances and periods of time. By contrast, the quantum computations that make encryption vulnerable only have to last long enough to spit out an answer, which makes their scalability feasible. The most promising approaches I've seen in terms of quantum resistance seem to be along the lines of extremely clever zero knowledge proofs, which can be arranged such that party A can prove to party B that they know something particular that party B has agreed is sufficient authentication or authorization, without revealing to party B exactly what it is that party A knows.