caa a22 4500 52878580X 20190713030955.0 cr unu---uuuuu 180924s2015 xx s 000 0 eng 10.3929/ethz-b-000101960 doi 10.1038/ncomms8046 doi (ETHRESEARCH)oai:www.research-collection.ethz.ch:20.500.11850/101960 Measuring the dynamic structure factor of a quantum gas undergoing a structural phase transition [Elektronische Daten] [Renate Landig, Ferdinand Brennecke, Rafael Mottl, Tobias Ulrik; id_orcid 0000-0001-7016-587X Donner, Tilman Esslinger] Nat Commun Open access ethresearch The dynamic structure factor is a central quantity describing the physics of quantum many-body systems, capturing structure and collective excitations of a material. In condensed matter, it can be measured via inelastic neutron scattering, which is an energy-resolving probe for the density fluctuations. In ultracold atoms, a similar approach could so far not be applied because of the diluteness of the system. Here we report on a direct, real-time and nondestructive measurement of the dynamic structure factor of a quantum gas exhibiting cavity-mediated long-range interactions. The technique relies on inelastic scattering of photons, stimulated by the enhanced vacuum field inside a high finesse optical cavity. We extract the density fluctuations, their energy and lifetime while the system undergoes a structural phase transition. We observe an occupation of the relevant quasi-particle mode on the level of a few excitations, and provide a theoretical description of this dissipative quantum many-body system. Creative Commons Attribution 4.0 International http://creativecommons.org/licenses/by/4.0 ethresearch Landig Renate joint author Brennecke Ferdinand joint author Mottl Rafael joint author Donner Tobias Ulrik; id_orcid 0000-0001-7016-587X joint author Esslinger Tilman joint author Nature Communications London : Nature Publishing Group 6, p. 7046 2041-1723 http://hdl.handle.net/20.500.11850/101960 text/html WWW-Backlink auf das Repository (Open access) 1 Journal Article ethresearch ETHRESEARCH 856 40 http://hdl.handle.net/20.500.11850/101960 text/html WWW-Backlink auf das Repository (Open access) ETHRESEARCH 700 1- Landig Renate joint author ETHRESEARCH 700 1- Brennecke Ferdinand joint author ETHRESEARCH 700 1- Mottl Rafael joint author ETHRESEARCH 700 1- Donner Tobias Ulrik; id_orcid 0000-0001-7016-587X joint author ETHRESEARCH 700 1- Esslinger Tilman joint author ETHRESEARCH 773 0- Nature Communications London : Nature Publishing Group 6, p. 7046 2041-1723 BK010053 XK010053 XK010000 ETHRESEARCH ETHRESEARCH ETHRESEARCH Journal Article Open access