Freiburg 2024 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 42: Long-range Interactions

Q 42.4: Talk

Thursday, March 14, 2024, 12:00–12:15, HS 1015

Bragg Spectroscopy of a Dynamic Instability where two soft modes meet. — Alexander Baumgaertner, Gabriele Natale, •Justyna Stefaniak, Simon Hertlein, David Baur, Dalila Rivero, Tobias Donner, and Tilman Esslinger — ETH Zurich, Switzerland

The excitation spectrum of open many-body systems can give rise to various features e.g. dynamical instabilities and exceptional points. In our experiment, consisting of a Bose-Einstein condensate (BEC) coupled to a cavity mode, we realize two different superradiant crystals and perform Bragg spectroscopy to measure the excitation spectrum. Long-range interactions in quantum gases can give rise to an excitation spectrum with a roton-type minimum in the dispersion relation. In our case, we associate a roton-like mode with each of the superradiant crystals. By changing interaction strength, we observe how the excitation energies, the strength of the density-density correlations and the roton momentum are modified prior to the formation of one of the crystal phases. Dissipation introduces coupling between these two modes and can lead to an amplification of one and a dampening of the other mode. Additionally tuning the strength of the interactions, we found a regime, where two roton-type modes respond at the same energy. In this regime, the presence of dissipation introduces a coupling between these two models and finally leads to a dynamic instability of the system.

Keywords: cavity, instability, roton, self-organisation