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Zenith Grant Awardee

Gregor Weihs

University of Innsbruck


Caslav Brukner, University of Vienna

Project Title

Higher-order Interferences and Time in Alternatives to Quantum Theory

Project Summary

Quantum theory has been with us for about a century almost in its present form. While it provides us with excellent tools to calculate the inner workings of matter and the power to create technology that we would have termed science fiction only a few years ago there are still many things that we don't understand about it – why is quantum theory the way it is? Furthermore, quantum theory seems to resist our desire to unify it with a description of gravity – Could we modify quantum theory to make it compatible?

In our project, we will explore some alternatives to quantum theory and quantum theory with small modifications. Theoretical studies and quantum optical experiments will show us whether these alternatives and modifications could be consistent with what we find in nature. If so, our findings may point us in the right direction for a unified theory, or the understanding of the quantum classical boundary. If, instead, we find that these alternatives can be refuted, we will know that we have to focus our efforts elsewhere.

Technical Abstract

Quantum mechanics appears to be a rigid island in theory space that doesn't allow for small modifications without ruining the whole construct. And yet, it seems clear that without such modifications we won't see a quantum theory of gravitation. In this project, we will explore the sea around this island by investigating alternative probabilistic theories with modified probability rules and / or modified state representation using hypercomplex numbers.

In our theory work we will elucidate the properties of theories based on quaternion and other hypercomplex numbers and design interferometric tests of these theories vs. standard quantum mechanics. We will further examine the role of time in theories that could possess multiple timelike dimensions. Finally we will look into simulations of such higher-level theories using ordinary quantum mechanics to analyze computational complexity in the light of varying representations of information.

On the experimental side, we will use our expertise gained in triple slit experiments in order to improve the bound on deviations from Born's rule or the presence of multi-order interference. Theories based on hypercomplex numbers can be tested using similar experiments and we will implement these tests, once they have been sufficiently refined in the theory part.

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