# Research Interests

### Characterising Quantum Phenomena

One of the most striking discoveries of last century is that Nature is incompatible with classical physics. Nonlocality [1], Contextuality [2] and Steering [3,4] 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 [5]. My research pursues an understanding of which nonclassical properties Nature may display, and how quantum theory features them.

### A theory beyond Quantum

Quantum theory is currently our most accurate description of Nature, at least in the microscopic scale. Nevertheless, whether quantum theory is the ultimate theory of Nature remains unclear. One of the main reasons for this is the tension it displays with the theory of General Relativity. Indeed, both theories differ in crucial fundamental aspects, such as the role of “time”. Traditional approaches to resolving this tension, such as String Theory, have preserved the structure of quantum theory whilst modifying General Relativity [6]. However, recent insight has suggested the need to radically modify both theories [7]. Hence, quantum theory, and with it its applications, cannot be taken for granted, and it is therefore imperative that we explore the possibilities beyond it. My research seeks answers to how sensible deviations of quantum theory would look like, which nonclassical features they may have, and how nonquantum they may be, all within the promising framework of process theories [8].

### Identifying and optimizing computational power

Quantum computers carry the promise of unparalleled computational power, offering dramatic speed-up relative to their classical counterparts. However, a precise delineation of the power and limitations of quantum computation is still lacking. I aim to research the source, the structure, and the extent of advantage offered by quantum resources (such as contextuality) in quantum computation by exploring how to quantify the cost of resources and then optimize their use. I intend to leverage resource-theoretic approaches to quantum resources to explore the range of applicability of current benchmarks of quantum advantage. I am particularly interested in photonic implementations of quantum computation.

### Causal discovery

Does smoking cause cancer? How to answer such a question has been in the minds of people for centuries. Formally, this is explored in the field of causal inference, whose main goal is to understand how to identify the cause-effect relations among a set of variables/systems given their statistical data (called the “causal discovery” problem). This plays a crucial role in a variety of fields, such as medicine, epidemiology, finance, and climate change, to name a few. The relation between the quantum information and causality communities goes both ways: by exporting techniques and ideas from quantum information, the field of classical causal inference has gained new tools for classical discovery. Conversely, the perspective from causal inference has provided insight on the causal mechanisms that could enable Bell inequality violations. In addition, substantial progress has been made on the understanding of “what is happening” (causality) vs. “what an agent believes that is happening” (inference). This has led to the development of a deeper understanding of non-classical aspects of nature, and was enabled by the development of the so-called causal-inferential theories formalism. My goal is to combine newly-developed tools from the fields of causation and inference, and apply them to the causal discovery problem. I'm particularly interested in the question of how to propose intrinsically quantum notions of causation and inference. I'm also interested in how to design algorithms that can leverage these quantum notions to identify the possibly cause-effect relations underpinning physical systems or variables.

### Harnessing nonclassicality for information processing

Nonclassical features of quantum theory are known to enable information processing beyond our classical capabilities. Some have been explored in depth, such as the case of nonlocal correlations in Bell scenarios, which power secure quantum cryptography [9]. Other phenomena have only been recently explored, as is the case of Steering and Contextuality. Steering, for instance, enables a quantum advantage in semi-device-independent paradigms of quantum cryptography [10]. Contextuality, on the other hand, may power Measurement Based Quantum Computing [11,12], and is a necessary resource for universal quantum computation via magic state distillation [13]. My research aims at understanding and harnessing nonclassicality as a resource: how nonclassical properties of Nature, featured by quantum theory, may power technologies beyond what’s classically possible.

### Nonclassicality in the macroscopic realm

A fundamental problem is to understand how classicality emerges from quantum theory in the macroscopic world. An aspect of this open question is that of witnessing nonclassicaliy in many-body systems, where the number of constituents may be arbitrarily large. This in turn is of particular interest when thinking of nonclassical systems as scalable resources for information processing [14]. My research explores how to certify nonclassicality in many-body systems from the information accessible via our current experimental capabilities.

### References

[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). [4] H. M. Wiseman, S. J. Jones, and A. C. Doherty, Phys. Rev. Lett. 98:140402 (2007).[5] S. Popescu and D. Rohrlich, Found. Phys. 24:379 (1994).[6] J. Polchinski, “String theory”. C. U. Press, 1998. [7] L. Hardy, J. Phys. A 40, 3081 (2007).[8] B. Coecke and A. Kissinger. Picturing Quantum Processes: A First Course in Quantum Theory and Diagrammatic Reasoning. CUP, 2017.[9] N. Brunner et al. Rev. Mod. Phys., 86:419, 2014.[10] D Cavalcanti and P Skrzypczyk. Rep. Prog. Phys., 80:024001, 2017.[11] J. Anders and D. E. Browne. Phys. Rev. Lett., 102:050502, 2009.[12] R. Raussendorf. Phys. Rev. A, 88:022322, 2013.[13] M. Howard et al. Nature, 510:351, 2014. [14] M. Lewenstein, A. Sanpera, and V. Ahufinger. Ultracold Atoms in Optical Lattices: Simulating quantum many-body systems. Oxford University Press, 2012.