title: Almost quantum correlations.
abstract: Quantum theory is not only successfully tested in laboratories every day but also constitutes a robust theoretical framework: small variations usually lead to implausible consequences, such as faster-than-light communication. It has even been argued that quantum theory may be special among possible theories. Here we report that, at the level of correlations among different systems, quantum theory is not so special. We define a set of correlations, dubbed 'almost quantum', and prove that it strictly contains the set of quantum correlations but satisfies all-but-one of the proposed principles to capture quantum correlations. We present numerical evidence that the remaining principle is satisfied too.
authors.affiliation: 1] Department of Physics, Bilkent University, Ankara 06800, Turkey [2] Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain [3] H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
authors.forename: Miguel
authors.initials: M
authors.lastname: Navascués
authors.affiliation: H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
authors.forename: Yelena
authors.initials: Y
authors.lastname: Guryanova
authors.affiliation: 1] ICFO-Institut de Ciencies Fotoniques, 08860 Castelldefels (Barcelona), Spain [2] Department of Computer Science, University of Oxford, Parks Road, Oxford OX1 3QD, UK.
authors.forename: Matty J
authors.initials: MJ
authors.lastname: Hoban
authors.affiliation: 1] ICFO-Institut de Ciencies Fotoniques, 08860 Castelldefels (Barcelona), Spain [2] ICREA-Institucio Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Acín