On 02/06/2026, at 1:15 PM, in room 2011 of the Faculty of Physics, University of Białystok, mgr Karthik Eswaran, from the Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, will give a lecture entitled:
„Photonic time crystals in Bose-Einstein condensates”
Andrzej Maziewski
Jerzy Przeszowski
„Photonic time crystals in Bose-Einstein condensates”
mgr Karthik Eswaran
Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University
Photonic time crystals (PTCs) are spatially homogeneous media whose electromagnetic properties are periodically modulated in time. In contrast to ordinary photonic crystals, where spatial periodicity produces band structures in momentum space, temporal periodicity gives rise to Floquet quasi-energy bands with nontrivial time-domain topology, momentum gaps, time reflection and refraction, and dynamical instabilities. Despite substantial theoretical progress, realizing photonic time crystals at optical frequencies remains a significant challenge. In this talk, I will introduce a homogeneous Bose–Einstein condensate with periodically modulated interaction strength as an analogue platform for PTC physics. Starting from the Gross–Pitaevskii equation, the Bogoliubov excitations of the condensate can be mapped onto the wave equation of a temporally modulated optical medium, with the interaction strength playing the role of an effective time-dependent dielectric response. This correspondence allows the effective PTC band structure to be probed through the momentum distribution of the Bose gas obtained by time-of-flight imaging of atoms released from the trap after modulation. More generally, it suggests the use of driven ultracold atomic systems as an ideal platform for the study of time-varying media, which are of a broader theoretical interest. I will briefly discuss extensions of this platform, including localized oscillating perturbations as analogues of emitters embedded in a photonic time crystal, temporal edge-state physics and a topological stabilization protocol. Finally, an optical lattice implementation will be discussed as a possible route toward strongly interacting regimes beyond the grasp of mean-field theory. If time permits, Anderson localization in time induced by controlled temporal disorder will also be discussed
