Laboratoire Kastler Brossel, Sorbonne Université, CNRS, ENS-PSL Research University, Collège de France, Paris 75005, France.
Phys Rev Lett. 2018 Nov 2;121(18):183604. doi: 10.1103/PhysRevLett.121.183604.
Quantum fluids of light are a photonic counterpart to atomic Bose gases and are attracting increasing interest for probing many-body physics quantum phenomena such as superfluidity. Two different configurations are commonly used: the confined geometry where a nonlinear material is fixed inside an optical cavity and the propagating geometry where the propagation direction plays the role of an effective time for the system. The observation of the dispersion relation for elementary excitations in a photon fluid has proved to be a difficult task in both configurations with few experimental realizations. Here, we propose and implement a general method for measuring the excitations spectrum in a fluid of light, based on a group velocity measurement. We observe a Bogoliubov-like dispersion with a speed of sound scaling as the square root of the fluid density. This Letter demonstrates that a nonlinear system based on an atomic vapor pumped near resonance is a versatile and highly tunable platform to study quantum fluids of light.
光量子流体是原子玻色气体的光子对应物，对于探测多体物理量子现象（如超流性）越来越引起人们的兴趣。通常使用两种不同的配置：受限几何形状，其中非线性材料固定在光学腔体内；传播几何形状，其中传播方向在系统中起到有效时间的作用。在这两种配置中，观察光子流体中基本激发的色散关系一直是一项艰巨的任务，仅有少数实验实现。在这里，我们提出并实现了一种基于群速度测量的测量光流体中激发谱的通用方法。我们观察到类似于玻色子的色散，其声速与流体密度的平方根成正比。这封信件表明，基于原子蒸气的近共振泵浦的非线性系统是研究光量子流体的多功能且高度可调谐的平台。
