 # Details of Grant

EPSRC Reference: EP/W024500/1
Title: Multidimensional moment problems and the quantum-classic divide
Principal Investigator: Kimsey, Dr D
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: Sch of Maths, Statistics and Physics
Organisation: Newcastle University
Scheme: Standard Research - NR1
Starts: 01 October 2022 Ends: 30 September 2023 Value (£): 98,551
EPSRC Research Topic Classifications:
 Algebra & Geometry Mathematical Analysis
EPSRC Industrial Sector Classifications:
 No relevance to Underpinning Sectors
Related Grants:
Panel History:
 Panel Date Panel Name Outcome 08 Dec 2021 EPSRC Mathematical Sciences Small Grants Panel December 2021 Announced
Summary on Grant Application Form
Imagine you are given a graph that gives you the distribution of child heights in a school. From it you could easily calculate the average height of the children. With a bit more work you could calculate the typical variation of heights about that average. These two quantities -- the mean and the variance -- are the first two in a sequence of numbers, known as the moments of the probability distribution. They give important information about the shape of the probability distribution graph (e.g., where its "middle" is in the the case of the mean).

Whilst going from a probability distribution to the collection of moments is trivial, going in the other direction is not so simple. If one has access to the complete (in principle infinite) set of moments, then reconstructing the distribution is no problem. However, what about the case when we are only given a finite set of moments? What can we say about the underlying distribution? Is there any guarantee that, given a set of moments, that such a distribution even exists?

These questions come under the title of the univariate truncated moment problem (TMP). And this is well understood from several different points of view (e.g., matrix theory, operator theory, probability theory and optimisation theory). However, multidimensional analogues of the TMP, where the given finite list is multiply indexed and we are worried about the probability of several different things happening, have proven to be much more elusive. Standard approaches that are known to work for in the univariate setting are inadequate in the multidimensional setting (insofar, as the discovery of concrete necessary and sufficient conditions for a solution are only understood in a few limited settings). The progress so far made with multidimensional TMPs has stimulated advances in function theory, operator theory and real algebraic geometry. Applications for multidimensional TMPs are in full abundance, e.g., probability theory, signal processing and theoretical physics.

With applications in mind, we have identified an important and as-yet unexplored connection between multidimensional TMPs and foundational questions in quantum theory. In particular, we assert that the question of the existence of solutions to the TMP where the measure is supported on a given finite set is fundamental to understanding whether a set of observations is consistent with quantum or classical mechanics. Utilising recent advances in operator theory and real algebraic geometry, this project will develop new tools for solving these moment problems which will enable us to create a novel, unified and formally-rigorous framework for investigating the divide between classical and quantum theories.
Key Findings
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