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arXiv · 2607.28202

Purifications for Convex Cones

Felix Campidell·Tim Netzer
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Abstract

Motivated by the importance of the purification principle in quantum theory and generalized probabilistic theories, we study purifications using only the geometry of a finite-dimensional proper convex cone. We prove an existence theorem for indecomposable cones and intermediate tensor cones containing the maximally entangled state; in particular, every interior point of an indecomposable homogeneous cone admits a purification. This applies to Lorentz cones, for example. We also give a criterion for uniqueness up to local automorphisms. On the boundary, we show that if every proper face of $C$ is simplicial, then only pure points can admit purifications, and we demonstrate that this conclusion fails in the presence of non-simplicial faces. Examples involving positive semidefinite cones, Lorentz cones, $k$-positive maps, PPT tensors, and polyhedral cones illustrate both existence and non-uniqueness phenomena.

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Felix Campidell, Tim Netzer. 2026-07-30. Purifications for Convex Cones. https://arxiv.org/abs/2607.28202

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