We report the analysis of paired photon pulses arising from two cascading transitions in continuously pumped erbium-doped ${\mathrm{YLiF}}_4$ 1% and 0.01% crystals at 1.6 K. The dependence of the pulse peak intensity on the squared number of involved erbium ions, between ${10}^{11}$ and ${10}^{13}$, definitely identifies the cooperative nature of the two pulsed emissions, that are generated by the subsequent, spontaneous formation of coherent states. The observed fluctuations of the time interval between the paired pulses and, most importantly, its correlation with the second pulse duration demonstrate that the erbium ions coherence is indeed seeded by quantum fluctuations.

中文翻译：

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Er：YLF中的级联超荧光

我们报告了在连续泵浦掺中两个级联跃迁产生的成对光子脉冲的分析 ${\mathrm{锂离子电池}}_4$ 在1.6 K时有1％和0.01％的晶体。脉冲峰值强度与所含离子平方数的关系在 ${10}^{11}$ 和 ${10}^{13}$明确地确定了两个脉冲发射的合作性质，这是由相干态的随后自发形成所产生的。观察到的成对脉冲之间时间间隔的波动，最重要的是，它与第二个脉冲持续时间的相关性表明，quantum离子的相干性确实是由量子波动引起的。