Erlangen 2022 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 68: Quantum Cooperativity (joint session Q/SYQC)

Q 68.7: Vortrag

Freitag, 18. März 2022, 12:00–12:15, Q-H15

Cavity-induced long-range interactions in strongly correlated systems — •Paul Fadler¹, Jiajun Li², Kai Phillip Schmidt¹, and Martin Eckstein¹ — ¹Friedrich-Alexander Universität Erlangen-Nürnberg — ²Paul Scherrer Institut

In recent years, the coupling of optical cavity modes to solid states systems has emerged as a possible way to control material properties. Here we investigate cavity-induced long-range interactions between spins in a Mott insulator, which are a new feature of the coupling to the quantized cavity field and are absent in the control of magnetism by classical light. In detail, we show that coupling a cavity mode to the Fermi-Hubbard model at half filling leads to long-range four-spin terms in the effective low spin model at large onsite-interaction U, in addition to the conventional local antiferromagnetic Heisenberg exchange interaction. To obtain these long-range interactions, we compare exact diagonalization, a perturbative approach based on the effective spin-photon Hamiltonian description of the system, and fourth-order perturbation theory in the Hubbard model. We show that knowing the phenomenologically determined spin-photon matrix elements is not sufficient to derive the photon-mediated spin-interactions; instead, long-range interactions are additionally mediated via virtual intermediate states, that involve multiple excitations in the charge sector. A similar point should be kept in mind for deriving photon-mediated long-range interactions between emergent low-energy degrees of freedom in interacting systems in general.