Community Research and Development Information Service - CORDIS


NLST Report Summary

Project ID: 291574
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Final Report Summary - NLST (Nonlocality in space and time)

Quantum mechanics, the theory that describes the behaviour of microscopic particles (atoms, molecules, subatomic particles) is our best theory of nature - it explains every experimental result with unprecedented accuracy. Yet, although its basic laws are known for almost nine decades there is an almost universal consensus that we still do not have a deep understanding of its nature. Unexpected and almost paradoxical new results are discovered with disconcerting frequency – they are paradoxical only because we do not yet have the conceptual tools to expect them. Recently however it started to become apparent that part of the reason that quantum mechanics is so counter-intuitive is that nature is non-local. Understanding non-locality is then the way to get a better understanding of nature – this is the central idea of the project.

The project developed in two directions: work on non-locality, the main theme of the proposal, and work along new directions that opened during the project. The main results are as follows.

We found a number of new quantum paradoxes. One of them, that we called the “Quantum Cheshire Cat”, shows that properties can be disembodied from the particle that possesses them (such as separating the spin from a spinning particle) just like the smile from the Cheshire Cat. Another one, “Quantum violations of the pigeonhole principle”, (which was awarded the Cozzarelli Prize 2016 for “scientific excellence and originality”) shows how three particles could be put in two boxes, in such a way that no box contains more than one particle. Both paradoxes are related to non-locality in time and use a special technique called “pre- and post-selection”.

On a deeper conceptual level we proposed a new view on the nature of time, following the philosophical idea of “each moment of time a new universe”. In this approach subsequent moments of time are correlated (entangled) in non-local ways and the flow of time is the result of these correlations. We also proposed a comprehensive framework for investigating time non-locality.

We have also investigated how much basic facts about Nature, such as the impossibility of sending messages backward in time or faster than the speed of light, constrain the laws of physics. It has been known already that there other possible theories, different from quantum mechanics, that respect them. The question is what other natural physical and information-theoretic constraints should be added which would imply the mathematical formalism of quantum mechanics? Viewing quantum mechanics in this larger framework, contrasting it with other possible theories that all predict the same basic things about nature, allows us to see what is special about it. In this direction, focusing on non-locality in space, we discovered that theories that lead to what we called “Almost Quantum Correlations” obey all the constraints suggested so far, yet are different from quantum mechanics; if one day experiments will show that quantum mechanics is not a correct representation of nature, a theory yielding “almost quantum correlations” seems a natural candidate. In a different direction we proposed the existence of an information unit as a postulate that singles out quantum mechanics.

Furthermore, concerning non-locality in space, we made significant progress in understanding different manifestations of this phenomenon. A significant amount of work was done on “non-local steering”, by which the state of one of one member of a pair of correlated particles can changed remotely, by acting on its partner., and we uncovered new quantitative aspects of this effect. Some of our other results on non-local correlations in space have immediate applications in for information processing, including cryptographic settings (sending secret messages) and building random number generators that are used in many applications.

One of the major new directions followed in this project involves quantum thermodynamics. Thermodynamics – one of the major areas of physics - was originally invented to deal with macroscopic thermal machines such as steam engines, long before microscopic particles, let alone the theory of quantum mechanics, were discovered. We made significant progress by extending thermodynamics to individual quantum systems showing that essentially the same laws apply to individual microscopic quantum systems as for macroscopic ones. In a different direction, we have investigated the role of entanglement and non-locality in biological systems – a problem that has received considerable interest recently.

Finally, in a recent work still under review, we studied the issue of conservation laws – some of the most important laws of Nature. We raised fundamental questions about the very meaning of conservation laws in quantum mechanics and we argued that the standard way of defining them, while perfectly valid as far as it goes, misses essential features of nature and has to be revisited and extended.

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