Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Phys Rev Lett. 2011 Jun 24;106(25):255302. doi: 10.1103/PhysRevLett.106.255302. Epub 2011 Jun 22.
Using an angle-resolved heterodyne four-wave-mixing technique, we probe the low momentum excitation spectrum of a coherent polariton gas. The experimental results are well captured by the Bogoliubov transformation which describes the transition from single particle excitations of a normal fluid to soundlike excitations of a superfluid. In a dense coherent polariton gas, we find all the characteristics of a Bogoliubov transformation, i.e., the positive and negative energy branch with respect to the polariton gas energy at rest, soundlike shapes for the excitations dispersion, intensity, and linewidth ratio between the two branches in agreement with the theory. The influence of the nonequilibrium character of the polariton gas is shown by a careful analysis of its dispersion.
我们使用角度分辨外差式四波混频技术，探测相干极化激元气体的低动量激发谱。实验结果与描述正常流体中单粒子激发到超流声激发转变的玻色-爱因斯坦变换吻合得很好。在稠密的相干极化激元气体中，我们发现玻色-爱因斯坦变换的所有特征，即在极化激元气体静止能量下的正、负能支，激发色散的类似声子的形状，以及两分支之间的强度和线宽比都与理论相符。通过对色散的仔细分析，显示了极化激元气体非平衡性质的影响。
