Bromley S L, Zhu B, Bishof M, Zhang X, Bothwell T, Schachenmayer J, Nicholson T L, Kaiser R, Yelin S F, Lukin M D, Rey A M, Ye J
JILA, NIST and Department of Physics, University of Colorado, 440 UCB, Boulder, Colorado 80309, USA.
Université de Nice Sophia Antipolis, CNRS, Institut Non-Linéaire de Nice, UMR 7335, F-06560 Valbonne, France.
Nat Commun. 2016 Mar 17;7:11039. doi: 10.1038/ncomms11039.
We investigate collective emission from coherently driven ultracold (88)Sr atoms. We perform two sets of experiments using a strong and weak transition that are insensitive and sensitive, respectively, to atomic motion at 1 μK. We observe highly directional forward emission with a peak intensity that is enhanced, for the strong transition, by >10(3) compared with that in the transverse direction. This is accompanied by substantial broadening of spectral lines. For the weak transition, the forward enhancement is substantially reduced due to motion. Meanwhile, a density-dependent frequency shift of the weak transition (∼10% of the natural linewidth) is observed. In contrast, this shift is suppressed to <1% of the natural linewidth for the strong transition. Along the transverse direction, we observe strong polarization dependences of the fluorescence intensity and line broadening for both transitions. The measurements are reproduced with a theoretical model treating the atoms as coherent, interacting radiating dipoles.
我们研究了相干驱动的超冷（88）Sr原子的集体发射。我们进行了两组实验，分别使用对1 μK下原子运动不敏感和敏感的强跃迁和弱跃迁。我们观察到具有高度定向的向前发射，对于强跃迁，其峰值强度在横向方向上增强了>10³ 。这伴随着谱线的显著展宽。对于弱跃迁，由于原子运动，向前增强显著降低。同时，观察到弱跃迁的密度依赖频率 shift（约为自然线宽的10%）。相比之下，对于强跃迁，这种 shift 被抑制到自然线宽的<1%。在横向方向上，我们观察到两种跃迁的荧光强度和线展宽都有很强的偏振依赖性。测量结果用一个将原子视为相干、相互作用的辐射偶极子的理论模型进行了再现。
