How do you measure a Fermionic Quantum Field as a Theorist? -- Unruh-DeWitt-type Particle Detector Models for Scalar and Spinor Fields

Talk

In theoretical physics, there is multitude of different mathematical methods how to explore the properties of a quantum field. Among these, particle detector models have become a popular choice in diverse fields, including Cosmology, Quantum Optics, and both relativistic and non-relativistic Quantum Information Theory. Particularly prevalent is a model that DeWitt introduced in 1979, based on Unruh's seminal 1976 paper on black-hole radiation. This model, often dubbed the "Unruh-DeWitt detector", couples a simple two-level system to a scalar quantum field. It offers the double advantage of mathematical simplicity while allowing physical intuition. Currently, it is widely being applied: to explore the famous Unruh-effect, as sender and recipient of information, and even as a model for matter-light interaction to name a few. The Unruh-DeWitt detector is limited to scalar fields. However, in nature more complex fields are ubiquitous: fermionic particles like leptons and quarks, as well as vector bosons such as photons are the key components of the matter surrounding us! It is therefore natural to ask: can a concept comparable to the Unruh-DeWitt detector be developed for these quantum fields as well? In this talk, the concept of Unruh-DeWitt-type particle detector models will be revisited, before developing an Unruh-DeWitt-type particle detector model for spinor fields. A renormalisation scheme at first order in perturbation theory will be introduced. Finally, it will be demonstrated how to derive Feynman rules and use full-fledged Feynman diagrams to handel Unruh-DeWitt-type particle detector models to arbitrary order in perturbation theory. This provides a powerful framework for applying the new spinor field detector to address open questions like entanglement measures for fermionic fields.

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