Speaker
Description
The topic of particle localisation, namely how one defines a position operator or centre of mass in relativistic quantum mechanics, has been a longstanding question in the foundations of quantum mechanics since the mid-20th century. However, despite the length and breadth of study, the localisation problem is still not well understood.
I examine the implications of particle localisation in the Unruh-DeWitt model, which provides a simple model of a two-level system (aka 'particle detector') coupled to a scalar quantum field. By comparing the first- and second-quantised formulations of a detector with a quantised centre of mass, one is naturally led to two distinct notions of localisation. I consider the consequences of these two localisation schemes in the context of spontaneous emission, finding that the two localisations lead to distinguishable physical consequences, which can in principle be tested by future experiments.
