Landig Renate, Brennecke Ferdinand, Mottl Rafael, Donner Tobias, Esslinger Tilman
Institute for Quantum Electronics, ETH Zürich, CH-8093 Zürich, Switzerland.
Physikalisches Institut, University of Bonn, Wegelerstrasse 8, 53115 Bonn, Germany.
Nat Commun. 2015 May 6;6:7046. doi: 10.1038/ncomms8046.
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.
动态结构因子是描述量子多体系统物理性质的核心量，它能捕捉材料的结构和集体激发。在凝聚态物质中，可通过非弹性中子散射来测量动态结构因子，非弹性中子散射是一种用于探测密度涨落的能量分辨探针。在超冷原子领域，由于系统的稀薄性，到目前为止还无法应用类似的方法。在此，我们报告了对一种呈现腔介导长程相互作用的量子气体的动态结构因子进行的直接、实时且无损的测量。该技术依赖于由高精细度光学腔内增强的真空场激发的光子非弹性散射。在系统经历结构相变时，我们提取了密度涨落、其能量和寿命。我们观察到在几个激发态水平上相关准粒子模式的占据情况，并对这个耗散量子多体系统进行了理论描述。
