Seminar: Bayesian inference for quantum sensors and open quantum systems

Wednesday 25 November 4pm
Location: MS Teams
Speaker: Dr Ricardo Puebla, CTAMOP, Queen’s University Belfast


Inference techniques built on the Bayes’ theorem provide powerful tools for hypothesis testing and/or parameter estimation. In spite of other inference techniques, Bayesian inference deals with a probabilistic description of the key quantities to be determined. This is done by updating any prior information or knowledge according to the likelihood between the given set of observations and the proposed model to explain them. Such Bayesian techniques are routinely employed in many branches of science, and have been proven very useful in situations with a reduced number of observations and/or complex underlying models.

In this seminar I will review the main ingredients of Bayesian analysis and how to apply these techniques to quantum mechanical systems. In particular, I will discuss two illustrative and practical examples to showcase the suitability of Bayesian inference in quantum systems, namely, (i) an atomic-size quantum sensor aiming at detecting electromagnetic fields, and (ii) the inference of the environment properties of an open quantum system.

Positron binding as a molecular thermometer

Wednesday 28 October 3pm
Location: MS Teams
Speaker: Dr Andrew Swann, Queen’s University Belfast


The ability of many atoms and molecules to bind a positron has been recognized for over 20 years. Measurements of positron binding and annihilation have been carried out for around 90 molecules, although on the side of theory, ab initio calculations have proved to be difficult. Here, a model-potential approach is used to calculate the positron binding energy for n-alkanes (C_nH_{2n+2}) and the corresponding cycloalkanes (C_nH_{2n}). For n-alkanes, the dependence of the binding energy on the conformation of the molecule is investigated, with more compact structures showing greater binding energies. As a result, thermally averaged binding energies for larger alkanes (n > 9) show a strong temperature dependence in the range of 100–600 K. This suggests that positron resonant annihilation can be used as a probe of rotational (trans-gauche) isomerization of n-alkanes. In particular, the presence of different conformers leads to shifts and broadening of vibrational Feshbach resonances in the annihilation rate, as observed with a trap-based low-energy positron beam.

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We are a Research Cluster of the School of Mathematics and Physics at Queen’s University Belfast in Northern Ireland. Our research interests are focused primarily on computational and theoretical physics.

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The Old Physics Building,
where CTAMOP is situated.