Laws of Nature Series -- Future of quantum foundations

0:00 Sandro Donadi: Collapse Models: State of the Art and Future Perspectives
1:02:09 Siddhant Das: Can we fix quantum arrival times before 2026?

0:00 Sandro Donadi: Collapse Models: State of the Art and Future Perspectives

Collapse models solve the measurement problem by modifying the Schrödinger equation, adding new terms which describe spontaneous localization in space of the wavefunction. Because of these additional terms, collapse models make different predictions compared to Quantum Mechanics, so they can be experimentally tested. In this talk, we will give an introduction to the most important collapse models and to the state of the art of the bounds on their phenomenological parameters, coming from different experiments. We then also discuss possible improvements of these bounds as well as theoretical developments of the models.

1:02:09 Siddhant Das: Can we fix quantum arrival times before 2026?

I will discuss the problem of predicting the arrival (or detection) time of a quantum particle on a detector surface that remains unresolved despite the time-honoured empirical successes of quantum mechanics. Given that arrival-time or time-of-flight (TOF) measurements are the quintessence of standard experimental techniques of atomic and particle physics, this is particularly striking. Drawing upon the early history of this issue, I will discuss many (disparate) theoretical predictions for the TOF distribution of a particle suggested in the literature. These are informed by various semi-classical heuristics, principles, extensions, or (for want of a better word) "interpretations" of quantum theory. Next, I will describe a so-called "back-wall" experiment---an arrival-time experiment developed in collaboration with my late (and truly great) advisor Prof. Detlef Dürr that can reliably distinguish the aforementioned proposals. A key feature of our set-up is that the particle is escaping a potential barrier (the back-wall) in the direction of a distant detector, as opposed to moving completely freely. Without the back-wall, most proposals become nearly indistinguishable, which renders usual experimental tests inconclusive. I will also describe a concrete ion-trap implementation of the back-wall experiment doable with present-day technology. Time permitting, I will mention a version of this experiment featuring a spin-1/2 particle as an electron whose de Broglie-Bohm analysis predicts, thanks to quantum backflow, intriguing spin-dependent arrival-time distributions hitherto unknown, demanding experimental inspection.