测量经历结构相变的量子气体的动态结构因子
Measuring the dynamic structure factor of a quantum gas undergoing a structural phase transition
摘要：
动力学结构因子是描述量子多体系统物理、捕获结构和材料的集体激发的中心量。在凝聚态物质中，它可以通过非弹性中子散射来测量，这是一种能量分辨密度波动的探针。在超冷原子中，由于系统的稀释性，类似的方法迄今还不能应用。在这里，我们报告了一个直接的，实时的和非破坏性的测量量子气体的动态结构因子表现出腔介导的远程相互作用。该技术依赖于光子的非弹性散射，由高精细光学腔内部的增强真空场激发。我们提取的密度波动，他们的能量和寿命，而系统经历了结构相变。我们观察到占领的相关准粒子模式的水平上的几个激发，并提供了一个理论描述这个耗散量子多体系统。
英文摘要：
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 due to the diluteness of the system. Here, we report on a direct, real-time and non-destructive 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.
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