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Q: Fachverband Quantenoptik und Photonik

Q 11: QED and Cavity QED

Q 11.1: Talk

Monday, March 10, 2025, 17:00–17:15, HS Botanik

To infinity and back - 1/N graph expansion of light-matter systems — •Andreas Schellenberger and Kai Phillip Schmidt — FAU Erlangen-Nürnberg, Erlangen, Deutschland

We present a method for performing a full graph expansion for light-matter systems, utilizing the linked-cluster theorem. This enables us to explore 1/N corrections to the thermodynamic limit N→ ∞, giving us access to the mesoscopic regime. This region is yet largely unexplored, as it is challenging to tackle with established solid-state methods. However, it hosts intriguing features, such as entanglement between light and matter that vanishes in the thermodynamic limit [1-3]. We calculate physical quantities of interest for paradigmatic light-matter systems like generalized Dicke models by accompanying the graph expansion by both exact diagonalization (NLCE [4]) and perturbation theory (pcst++ [5]), benchmarking our approach against other techniques.

[1] J. Vidal, S. Dusuel; EPL 74 817 (2006)

[2] K. Lenk, J. Li, P. Werner, M. Eckstein; arXiv:2205.05559 (2022)

[3] A. Kudos, D. Novokreschenov, I. Iorsh, I. Tokatly; arXiv:2304.00805 (2023)

[4] M. Rigol, T. Bryant, R. R. P. Singh; Phys. Rev. Lett. 97, 187202 (2006)

[5] L. Lenke, A. Schellenberger, K. P. Schmidt, Phys. Rev. A, 108 (2023)

Keywords: Light-matter system; 1/N expansion; Series expansion method; Full graph Expansion; Numerical linked cluster expansion