Institut Non Linéaire de Nice, CNRS and Université Nice Sophia Antipolis, 1361 route des Lucioles, 06560 Valbonne, France.
CAPES Foundation, Ministry of Education of Brazil, Brasília DF 70040-020, Brazil.
Phys Rev Lett. 2016 Feb 26;116(8):083601. doi: 10.1103/PhysRevLett.116.083601. Epub 2016 Feb 22.
Since Dicke's seminal paper on coherence in spontaneous radiation by atomic ensembles, superradiance has been extensively studied. Subradiance, on the contrary, has remained elusive, mainly because subradiant states are weakly coupled to the environment and are very sensitive to nonradiative decoherence processes. Here, we report the experimental observation of subradiance in an extended and dilute cold-atom sample containing a large number of particles. We use a far detuned laser to avoid multiple scattering and observe the temporal decay after a sudden switch-off of the laser beam. After the fast decay of most of the fluorescence, we detect a very slow decay, with time constants as long as 100 times the natural lifetime of the excited state of individual atoms. This subradiant time constant scales linearly with the cooperativity parameter, corresponding to the on-resonance optical depth of the sample, and is independent of the laser detuning, as expected from a coupled-dipole model.
自狄克关于原子系综自发辐射相干性的开创性论文发表以来，超辐射已经得到了广泛的研究。相反，亚辐射仍然难以捉摸，主要是因为亚辐射态与环境的耦合较弱，并且对非辐射退相干过程非常敏感。在这里，我们报告了在包含大量粒子的扩展和稀释冷原子样品中观察到的亚辐射。我们使用远失谐激光来避免多次散射，并在激光束突然关闭后观察时间衰减。在大部分荧光快速衰减后，我们探测到非常缓慢的衰减，时间常数长达单个原子激发态自然寿命的 100 倍。这个亚辐射时间常数与协同参数呈线性关系，与样品的共振光深度相对应，并且与激光失谐无关，这与偶极子耦合模型的预期相符。
