Promotionsvortrag Physik: „Excitations and quantum criticality of spin systems with long-range interactions“

Ankündigung des Promotionsvortrags von: Herrn Patrick Adelhardt

Long-range interactions in quantum spin systems can lead to fundamentally different and exotic phenomena compared to their short-range counterparts. They can give rise to new phases, sig-nificantly alter critical behavior and low-energy spectral properties, promote entanglement, and dramatically change the propagation of information. Beyond their theoretical significance, these interactions naturally emerge in highly controllable atomic, molecular, and optical (AMO) quantum simulators. Due to the tremendous experimental advancements in recent years and their theoret-ical importance, long-range interacting systems have become a vibrant and impactful area of re-search.

In this talk, I begin with an introduction to quantum spin systems and their quantum critical behav-ior. I then present the method of perturbative continuous unitary transformation (pCUT) employed as a linked-cluster expansion. In particular, calculating the perturbative contributions on graphs and the subsequent embedding procedure allows to determine the elementary excitation gap and its critical properties in the thermodynamic limit.

In the second part, I highlight how long-range interactions fundamentally modify critical behavior, giving rise to distinct critical regimes absent in short-range models. I discuss the challenges they introduce, including the need to adapt the embedding step via Monte Carlo summation. Finally, I show how this approach can be used to uncover the quantum-critical properties of long-range spin models, demonstrating the interplay of spontaneous symmetry breaking and long-range interac-tions.

(Vortrag auf Englisch)

Dem Vortrag schließt sich eine Diskussion von 15 Minuten an. Vortrag und Diskussion sind öffentlich. Diesen Verfahrensteilen folgt ein nicht öffentliches Rigorosum von 45 Minuten.