McKeever J, Boca A, Boozer A D, Buck J R, Kimble H J
Norman Bridge Laboratory of Physics 12-33, California Institute of Technology, Pasadena, California 91125, USA.
Nature. 2003 Sep 18;425(6955):268-71. doi: 10.1038/nature01974.
Conventional lasers (from table-top systems to microscopic devices) typically operate in the so-called weak-coupling regime, involving large numbers of atoms and photons; individual quanta have a negligible impact on the system dynamics. However, this is no longer the case when the system approaches the regime of strong coupling for which the number of atoms and photons can become quite small. Indeed, the lasing properties of a single atom in a resonant cavity have been extensively investigated theoretically. Here we report the experimental realization of a one-atom laser operated in the regime of strong coupling. We exploit recent advances in cavity quantum electrodynamics that allow one atom to be isolated in an optical cavity in a regime for which one photon is sufficient to saturate the atomic transition. The observed characteristics of the atom-cavity system are qualitatively different from those of the familiar many-atom case. Specifically, our measurements of the intracavity photon number versus pump intensity indicate that there is no threshold for lasing, and we infer that the output flux from the cavity mode exceeds that from atomic fluorescence by more than tenfold. Observations of the second-order intensity correlation function demonstrate that our one-atom laser generates manifestly quantum (nonclassical) light, typified by photon anti-bunching and sub-poissonian photon statistics.
传统激光器（从桌面系统到微观设备）通常在所谓的弱耦合 regime 下运行，涉及大量原子和光子；单个量子对系统动力学的影响可忽略不计。然而，当系统接近强耦合 regime 时情况就不再如此，在强耦合 regime 中原子和光子的数量可能会变得相当少。实际上，理论上已经对共振腔内单个原子的激光特性进行了广泛研究。在此，我们报告了在强耦合 regime 下运行的单原子激光器的实验实现。我们利用腔量子电动力学的最新进展，使得一个原子能够在光学腔内被隔离在一种状态下，即一个光子就足以使原子跃迁饱和。观察到的原子 - 腔系统的特性与常见的多原子情况在性质上有所不同。具体而言，我们对腔内光子数与泵浦强度的测量表明，激光发射没有阈值，并且我们推断腔模的输出通量比原子荧光的输出通量高出十倍以上。对二阶强度相关函数的观察表明，我们的单原子激光器产生明显的量子（非经典）光，其典型特征是光子反聚束和亚泊松光子统计。
