Uniqueness of Composition in Quantum Theory and Linguistics

TL;DR

This paper proves a uniqueness result for the way systems can be composed in quantum theory and linguistics, showing that the standard structure is essentially the only option in a broad class of theories.

Contribution

It establishes that the canonical bilinear compact-closed symmetric monoidal structure is unique for a wide class of process theories, impacting quantum physics and computational linguistics.

Findings

Uniqueness of the monoidal structure in quantum theories.

Applicability to various quantum and toy theories.

Implication of a unique compatible grammar in linguistic models.

Abstract

We derive a uniqueness result for non-Cartesian composition of systems in a large class of process theories, with important implications for quantum theory and linguistics. Specifically, we consider theories of wavefunctions valued in commutative involutive semirings -- as modelled by categories of free finite-dimensional modules -- and we prove that the only bilinear compact-closed symmetric monoidal structure is the canonical one (up to linear monoidal equivalence). Our results apply to conventional quantum theory and other toy theories of interest in the literature, such as real quantum theory, relational quantum theory, hyperbolic quantum theory and modal quantum theory. In computational linguistics they imply that linear models for categorical compositional distributional semantics (DisCoCat) -- such as vector spaces, sets and relations, and sets and histograms -- admit an (essentially) unique compatible pregroup grammar.