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Zenith Grant Awardee

Sumati Surya

Raman Research Institute

Project Title

In Search of Covariant Quantum Information

Project Summary

The discovery of quantum theory a century ago marked a vast shift in physics with deterministic Newtonian laws being replaced by quantum probabilistic rules. Quantum theory has gained a wide respectability because of its spectacular experimental success and its ability to predict new phenomena including quantum computation, which is based on the ideas of quantum information. However, quantum theory possesses a basic dichotomy: its interpretation requires a classical \'observer\' who measures the quantum \'system\'. Since the theory works well in experimental situations this dichotomy has not hindered progress in manipulating quantum systems, in particular in quantum computation. However, from a theoretical viewpoint the dichotomy is deeply unsettling since quantum theory should also be used to describe the measuring device. In particular a functionalist approach cannot suffice while understanding a theory of the universe where there is no external classical observer to make measurements. How are we then to quantify the quantum information of the universe? This project is an attempt to begin to answer these questions within a measurement independent framework of quantum theory known as quantum measure theory.

Technical Abstract

If quantum information is indeed fundamental to our understanding of the physical world, then it must be possible to express quantum gravity as a theory of quantum information. However, the standard interpretation of quantum theory and hence quantum information requires the unsettling dichotomy between the classical measuring device and the quantum system. This is not tenable in quantum gravity – the early universe has no external classical observer who can supply us an interpretation of quantum probabilities. It is also desirable that quantum gravity should possess, in addition, a version of covariance. Thus the quantum information of the universe requires the formulation of a covariant measurement independent quantum theory. A promising approach is that of quantum measure theory and its realism-based interpretation of anhomomorphic logic. This is a histories-based approach where there is no recourse to measuring devices and in which quantum theory is seen as a generalised measure theory. It is the goal of this project to understand how quantum information manifests itself in this framework and whether it can in turn be used to give an information theoretic perspective on quantum gravity.

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