Mainz 2026 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 24: Ultra-cold Atoms, Ions and BEC I (joint session A/Q)

Q 24.6: Talk

Tuesday, March 3, 2026, 12:15–12:30, N 1

Spin and density order of ultracold two-component fermions coupled to an optical cavity — •Daniel Samoylov, Renan da Silva Souza, Youjiang Xu, and Walter Hofstetter — Goethe Universität, Institut für Theoretische Physik, 60438 Frankfurt, Germany

Ultracold two-component fermions coupled to a transversely pumped optical cavity experience cavity-mediated long-range interactions [1]. In the dispersive regime, when confined to a two-dimensional static optical lattice the steady states of this system can be described by an extended Hubbard Hamiltonian with long-range interactions mediated by the cavity photons. We use real-space dynamical mean-field theory (RDMFT) [2] to study the phase diagram of this system. We investigate the competition of the (superradiant) checkerboard density-wave (DW) phase and the magnetically ordered spin-density-wave (SDW) phase at half filling. For small values of the Hubbard onsite interaction strength and the cavity-mediated long-range interaction strength we find a homogeneous paramagnetic phase. The full phase diagram of the system is obtained by varying the Hubbard onsite interaction strength and the cavity-mediated long-range interaction strength at a fixed low temperature. We identify a region of coexistence between the DW and SDW solutions obtained within RDMFT. The thermodynamic phase transition in this region is obtained by comparing the energies of the different RDMFT solutions.

[1] K. Roux et al., Nat. Commun., 11, 1, 2974 (2020)

[2] M. Snoek et al., New J. Phys. 10, 093008 (2008)

Keywords: Fermi-Hubbard Model; Optical Cavity; Long-range Interactions