Decoherence to quantum theory from a causally-indefinite post-quantum theory
Abstract
We find a process satisfying the axioms of hyper-decoherence which produces standard quantum theory from the theory of quantum boxes (higher-order quantum theory with the non-signalling tensor product). This hyper-decoherence map evades the no-go theorem of Lee and Selby by relaxing constraints on signalling to the past and the uniqueness of purifications. We discuss some natural opposing conclusions: that the existence of this map might be evidence of a genuine hyper-decoherence process producing causal quantum theory from its causally-indefinite higher-order theory; or that it serves as an indication that the axioms of hyper-decoherence might need careful re-consideration, especially regarding the subtle albeit central role that purity plays.
Cite
@article{arxiv.2511.02772,
title = {Decoherence to quantum theory from a causally-indefinite post-quantum theory},
author = {James Hefford and Matt Wilson},
journal= {arXiv preprint arXiv:2511.02772},
year = {2026}
}