无处不在的双光子
Two photons everywhere
AI总结：
本研究以共振荧光为例探讨双光子物理学，揭示双光子层面关联图景的独特特征及理论基础，指出远离光谱峰处的强光子关联可通过多光子观测探测，兼具基础研究与应用价值。
摘要：
我们以共振荧光这一特殊且热门的案例为例，对双光子物理学展开探讨。研究表明，干涉与关联的基本概念在双光子层面呈现出与单光子层面截然不同的独立图景，其关联图景通过覆盖系统可发射的所有可能频率，揭示出多种物理过程。这类图景通常呈现出光子聚束线与反聚束圆的特征。解释这些特征的理论体系建立在两大支柱之上：其一为频率分辨光子关联理论，其二为经典场与量子场的混合理论。尽管迄今为止的实验工作主要聚焦于光谱峰之间的关联，但在远离光谱峰处发射的光子之间也存在强关联，这类关联仅能通过多光子可观测量探测到。这些发现既可用于深化对量子光学过程的基础理解，也可通过利用这些此前未被发现的资源应用于相关领域。
英文摘要：
We discuss two-photon physics, taking for illustration the particular but topical case of resonance fluorescence. We show that the basic concepts of interferences and correlations provide at the two-photon level an independent and drastically different picture than at the one-photon level, with landscapes of correlations that reveal various processes by spanning over all the possible frequencies at which the system can emit. Such landscapes typically present lines of photon bunching and circles of antibunching. The theoretical edifice to account for these features rests on two pillars: i) a theory of frequency-resolved photon correlations and ii) admixing classical and quantum fields. While experimental efforts have been to date concentrated on correlations between spectral peaks, strong correlations exist between photons emitted away from the peaks, which are accessible only through multiphoton observables. These could be exploited for both fundamental understanding of quantum-optical processes as well as applications by harnessing these unsuspected resources.
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