**'Relativistic causality and information processing' - a project submitted to the NCN competition by the International Centre for the Theory of Quantum Technologies-has gained funding of over 3.4 million PLN. - 'We ask what are the absolutely fundamental limits on information processing in any reasonable physical theory. Also such, which ... do not exist yet,' - says prof. dr hab. Paweł Horodecki, head of the project.**

MAESTRO 13 is a competition for research projects addressed to experienced scientists. Projects aiming at pioneering scientific research, including interdisciplinary, important for the development of science, going beyond the current state of knowledge, which may result in scientific discoveries, have the biggest chance for funding.

As noted by scientists from the International Centre for Quantum Theory of Quantum Technologies UG, **stronger correlations in a given theory allow for better processing of information.** For instance, quantum mechanics allows for stronger correlations than classical mechanics (photons in entangled states break Bell's inequality, whereas correlations obtained by tearing a banknote and sending its fragments to two different cities do not break Bell's inequality), which translates, for instance, into the possibility of creating a cryptographic key and reducing communication complexity when calculating certain functions.

The question is, how strong correlations could be in nature? The realization of the project entitled 'Relativistic causality and information processing' will allow us to understand the fundamental limits on information processing in nature, which, as noted by scientists, is important not only from the perspective of discovering the fundamental laws of physics but also in the context of potential applications in cryptography or communication in outer space.

- *'Since 1994, hypotheses on, among others, the existence of stronger classes proposed by Popescu and Rohrlich were formed, such hypothetical correlations were studied quite intensively,'* - notes **prof. dr hab. Paweł Horodecki.** - *'Two years ago with dr. Ravishankar Ramanathan we generalised and partially studied, admittedly only on a certain example, the most general of the classes, which - apart from one modest article (Grunhaus, Rohrlich, Popescu, 1996) - nobody had dealt with before. Its essence is the minimal assumption on the physical theory in which they could appear.'*

Prof. Paweł Horodecki explains that there are only two requirements, that the arena of the theory should be the space-time known from Einstein's theory of relativity and that no contradictory time travel should appear (i.e. e.g. great-grandfather paradox, when someone goes back in time and makes it impossible for his great-grandfather to meet his great-grandmother, which would result in the non-existence of this someone who does it in his past). The absence of such contradictions is treated here as a condition for the meaningfulness of a given physical theory.

- *'It turned out that correlations fulfilling only the second condition may have puzzling combinations of features,'* - says prof. Paweł Horodecki. - *'A year ago, we published a paper that says that standard cryptographic protocols (classical or quantum) using such correlations cannot work, e.g., in the case of satellites, this would mean that with the help of appropriate combinations of positions in space-time, two cooperating intruders can always intercept a cryptographic key, provided that it was produced with the methods known so far.'*

The project will explore the information-theoretic properties of various theories beyond standard quantum mechanics. The principle of non-contradiction with relativistic causal structure, i.e. the absence of logical paradoxes, will be taken as a basic axiom.

- *'The essence of the project is to pose the general problem of information processing principles in any theory that forbids the above-mentioned paradoxes. In particular, the aim is to study the "information-theoretic power" of these correlations,'* - explains prof. Paweł Horodecki. - *'For example, one of the goals will be to check whether there are any other new cryptographic protocols that are secure, and to construct a physical model in which such correlations could manifest themselves.'*

The project entitled 'Relativistic causality and information processing' proposes some attempt to constructively solve a difficult problem concerning quantum correlations at the borderline of mathematics and physics - the Tsirelson problem. If the problem is solved, the scientists from UG will try to relate and compare the newly constructed quantum correlations in the process of solution with their hypothetical descriptions.

Financial resources allocated by NCN for the realisation of research projects within the MAESTRO 13 competition amount to PLN **20 million.**