Abstract
We solve a long-standing conjecture by Barker, proving that the minimal and maximal tensor products of two finite-dimensional proper cones coincide if and only if one of the two cones is generated by a linearly independent set. Here, given two proper cones \({\mathcal {C}}_1\), \({\mathcal {C}}_2\), their minimal tensor product is the cone generated by products of the form \(x_1\otimes x_2\), where \(x_1\in {\mathcal {C}}_1\) and \(x_2\in {\mathcal {C}}_2\), while their maximal tensor product is the set of tensors that are positive under all product functionals \(\varphi _1\otimes \varphi _2\), where \(\varphi _1|_{{\mathcal {C}}_1}\geqslant 0\) and \(\varphi _2|_{{\mathcal {C}}_2}\geqslant 0\). Our proof techniques involve a mix of convex geometry, elementary algebraic topology, and computations inspired by quantum information theory. Our motivation comes from the foundations of physics: as an application, we show that any two non-classical systems modelled by general probabilistic theories can be entangled.
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Notes
Alternatively, the reader will find at https://github.com/gaubrun/entangleability a SageMath script which checks the correctness of (7).
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Acknowledgements
We are very grateful to Kyung Hoon Han for several remarks which helped us clarifying the manuscript. We thank also Alexander Müller-Hermes for useful comments on some of the results. GA was supported in part by ANR (France) under the grant StoQ (2014-CE25-0003). LL acknowledges financial support from the European Research Council under the Starting Grant GQCOP (Grant no. 637352), from the Foundational Questions Institute under the grant FQXi-RFP-IPW-1907, and from the Alexander von Humboldt Foundation. CP is partially supported by Spanish MINECO through Grant No. MTM2017-88385-P, by the Comunidad de Madrid through grant QUITEMAD-CM P2018/TCS4342 and by SEV-2015-0554-16-3. MP acknowledges support from grant VEGA 2/0142/20, from the grant of the Slovak Research and Development Agency under contract APVV-16-0073, from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation - 447948357) and the ERC (Consolidator Grant 683107/TempoQ).
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Aubrun, G., Lami, L., Palazuelos, C. et al. Entangleability of cones. Geom. Funct. Anal. 31, 181–205 (2021). https://doi.org/10.1007/s00039-021-00565-5
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DOI: https://doi.org/10.1007/s00039-021-00565-5
Keywords and phrases
- Tensor product of cones
- Entangleability
- General probabilistic theories
Mathematics Subject Classification
- Primary: 52A20
- 47L07
- Secondary: 81P16