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# Ana Belen Sainz

Area of Research:

## Research Interests

One of the most striking discoveries of last century is that Nature is incompatible with classical physics. Nonlocality [1], Contextuality [2] and Steering [3] are manifestations of powerful correlations which cannot be explained in the classical world, although they arise naturally in quantum mechanics. Quantum theory, however, does not exploit these phenomena to their maximum, i.e even stronger correlations are theoretically conceivable while still complying with special relativity [4].

Correlations among different components of a physical system play an important role in both everyday life and cutting-edge technology. Indeed, the exploitation of nonlocal correlations led to the development of now commercial secure quantum key distribution [5], while contextual correlations provide the resource for upcoming quantum computers [6]. A better understanding of quantum physics is then essential to identify limitations and possibilities of quantum technologies.

My research hence focuses on trying to understand what is special about quantum theory regarding these nonclassical phenomena. In particular, it aims at identifying what physical laws render them quantum. I explore the limits in the strength of quantum phenomena, which ultimately may shed light on the reach that protocols based on quantum technologies may have.

Particular open problems include the following:

How to understand quantum correlations "from the outside", specially in device independent (i.e. Bell non locality) and one-way device independent (i.e. steering) setups. These scenarios are crucial when performing information tasks in a network if correlations are to be used in a reliable manner. A particular instance of this problem includes the development of a better understanding of almost quantum" correlations [7], of which quantum predictions is a strict subset.
A fundamental problem is to understand how classicality emerges from quantum theory in the macroscopic world. Along these lines lies the question of how nonclassical phenomena such as Bell non locality may be exhibited in many-body systems. A relevant problem is then how to witness non locality in these macroscopic setups.
The problem of causal inference is to determine if a given observed statistical data is compatible with some causal structure. In other words, it asks which hypotheses about the causal mechanism can explain the given distribution. Nowadays, partial solutions to this problem are used in the fields of medicine, bio-informatics, image processing, and experiments on quantum foundations. The incompatibility of quantum statistics with classical causal structures is a well established fact [1], however not much is known about general scenarios. An intriguing question is then how this notion of classical incompatibility can be used as a resource, and which networks provide potential grounds for a quantum advantage".

[1] J. S. Bell, Physics 1:195200 (1964).

[2] S. Kochen and E. P. Specker, J. Math. Mech. 17:5987 (1967).

[3] E. Schrödinger, Mathematical Proceedings of the Cambridge Philosophical Society 32:446452 (1936). H. M. Wiseman, S. J. Jones, and A. C. Doherty, Phys. Rev. Lett. 98:140402 (2007).

[4] S. Popescu and D. Rohrlich, Found. Phys. 24:379 (1994).

[5] A. Acín et al., Physical Review Letters 98:230501 (2007). S. Pironio et al., New Journal of Physics 11(4):045021 (2009). U. Vazirani and T. Vidick, Phys. Rev. Lett. 113:140501 (2014).

[6] Mark Howard, Joel Wallman, Victor Veitch and Joseph Emerson, Nature 510:351355 (2014).

[7] M. Navascués, Y. Guryanova, M. Hoban, and A. Acín, Nature Communications 6:6288 (2015).

## Positions Held

• 2014 - 2016. Quantum Information and Foundations group, HH Wills Physics Laboratory, University Of Bristol, UK. Postdoctoral Researcher
• 2014. ICFO-Institut de Ciencies Fotoniques, Castelldefels (Barcelona), Spain. Postdoctoral Researcher
• 2009 - 2014. ICFO-Institut de Ciencies Fotoniques, Castelldefels (Barcelona), Spain. PhD Student.

## Awards

• "Best Student who graduated in 2008 Award", Santander Rio Bank, Argentina, 2010.
• Spanish doctoral fellowship: FPU grant, 2009.
• "Best Student who graduated in 2008", Facultad de Matemática, Astronomía y Física, Universidad Nacional de Córdoba, 2009.

## Recent Publications

• James Vallins, Ana Belén Sainz and Yeong-Cherng Liang, "Almost quantum correlations and their refinements in a tripartite Bell scenario", Physical Review A 95, (2017) 022111. arXiv: 1608.05641.
• Ravishankar Ramanathan, Marco Túlio Quintino, Ana Belén Sainz, Gláucia Murta, Remigiusz Augusiak, "Tightness of correlation inequalities with no quantum violation", Physical Review A 95, (2017) 012139. arXiv: 1607.05714.
• Antonio Acín, Runyao Duan, David E. Roberson, Ana Bel Ìen Sainz and Andreas Winter, "A new property of the Lovász number and duality relations between graph parameters", Discrete Applied Mathematics 216, (2017) pp. 489-501. arXiv: 1505.01265.
• Ana Belén Sainz, Yelena Guryanova, Will McCutcheon, Paul Skrzypczyk, "Adjusting inequalities for detection-loophole-free steering experiments", Physical Review A 94, (2016) 032122. arXiv: 1606.03018.
• Ana Belén Sainz, Leandro Aolita, Nicolas Brunner, Rodrigo Gallego, Paul Skrzypczyk, "Classical communication cost of quantum steering", Physical Review A 94, (2016) 012308. arXiv: 1603.05079.
• Ana Belén Sainz, Nicolas Brunner, Daniel Cavalcanti, Paul Skrzypczyk, Tamás V Ìertesi, "Postquantum steering", Physical Review Letters 115, (2015) 190403. arXiv: 1505.01430.
• J. Tura, R. Augusiak, A. B. Sainz, B. Lücke, C. Klempt, M. Lewenstein, A. Acín, "Nonlocality in many-body quantum systems detected with two-body correlators", Annals of Physics 362, (2015) 370-423. arXiv: 1505.06740.
• Joe Henson and Ana Belén Sainz, "Macroscopic non-contextuality as a principle for Almost Quantum Correlations", Physical Review A 91, (2015) 042114. arXiv: 1501.06052.
• Antonio Acín, Tobias Fritz, Anthony Leverrier and Ana Belén Sainz, "A Combinatorial Approach to Nonlocality and Contextuality", Communications in Mathematical Physics 334, (2015) 533- 628. arXiv: 1212.4084.
• J. Tura, R. Augusiak, A. B. Sainz, T. V Ìertesi, M. Lewenstein and A. Acín, "Translationally invariant Bell inequalities involving only two-body correlators", Journal of Physics A: Mathematical and Theoretical 47, (2014) 424024. Special issue devoted to â50 years of Bell"s theorem". arXiv: 1312.0265.
• J. Tura, R. Augusiak, A. B. Sainz, T. V Ìertesi, M. Lewenstein and A. Acín, "Detecting nonlocality in many-body quantum states", Science 344, (2014) pp. 1256-1258. arXiv: 1306.6860.
• A. B. Sainz, T. Fritz, R. Augusiak, J. B. Brask, R. Chaves, A. Leverrier and A. Acín, "Exploring the Local Orthogonality Principle", Physical Review A 89, (2014) 032117. arXiv: 1311.6699.
• T. Fritz, A. B. Sainz, R. Augusiak, J. B. Brask, R. Chaves, A. Leverrier and A. Acín, "Local Orthogonality as a multipartite principle for quantum correlations", Nature Communications 4, (2013) 2263. arXiv: 1210.3018.
• "A channel-based framework for steering, non-locality and beyond", Matty J. Hoban and Ana Belén Sainz, arXiv: 1708.00750.
• "A formalism for steering with local quantum measurements", A. B. Sainz, L. Aolita, M. Piani, M. J. Hoban and P. Skrzypczyk, arXiv: 1708.00756.
• "Almost quantum correlations violate the no-restriction hypothesis", Ana Belén Sainz, Yelena Guryanova, Antonio Acín and Miguel Navascués, arXiv: 1707.02620.
• "Multipartite Composition of Contextuality Scenarios", Ana Belén Sainz and Elie Wolfe, arXiv: 1701.05171.
• Proceedings of the International School of Physics "Enrico Fermi" 191, 1, 505-535 (2016): Quantum Matter at Ultralow Temperatures. J. Tura, A. B. Sainz, T. Grass, R. Augusiak, A. Acín and M. Lewenstein, "Entanglement and Nonlocality in Many-Body Systems: a primer ". arXiv: 1501.02733.
• 10th International Workshop on Quantum Physics and Logic, Electronic Proceedings in Theoretical Computer Science 171, 63-70 (2014). Tobias Fritz, Anthony Leverrier and Ana Belén Sainz, "Probabilistic models on contextuality scenarios", arXiv: 1307.0145.