We study the time-resolved fluorescence spectrum in two-level systems interacting with an incident coherent field, both in the weak and intermediate coupling regimes. For a single two-level system in the intermediate coupling case, as time flows, the spectrum develops distinct features, that are not captured by a semi-classical treatment of the incident field. Specifically, for a field on resonance with the atomic transition energy, the usual Mollow spectrum is replaced by a four peak structure, and for a frequency that is half of the atomic transition energy, the time-dependent spectrum develops a second harmonic peak with a superimposed Mollow triplet. In the long-time limit, our description recovers results previously found in the literature. After analyzing why a different behavior is observed in the quantum and classical dynamics, the reason for the occurrence of a second harmonic signal in a two-level system is explained via a symmetry analysis of the total (electron and photon) system, and in terms of a three level system operating in limiting regimes. We find an increased second harmonic signal in an array of two-level systems, suggesting a superradiance-like enhancement for multiple two-level systems in cavity setups. Finally, initial explorative results are presented for two-level model atoms entering and exiting a cavity, which hint at an interesting interplay between cavity-photon screening and atomic dynamics effects.
Frequency- and time-resolved second order quantum coherence function of IDTBT single-molecule fluorescence
University of California, Berkeley（加州大学伯克利分校）；Kavli Energy Nanoscience Institute at Berkeley（伯克利卡弗里纳米科学能源研究所）；Max Planck Institute for Polymer Research（马克斯·普朗克聚合物研究所）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
Visualizing the emission of a single photon with frequency and time resolved spectroscopy
在量子物理学的黎明，维格纳和Weisskopf获得了一个完整的分析描述（一个\textit{photon portrait}）的单光子发射的两个能级系统，使用频率模式的基础（Weisskopf和维格纳，“Zeitschrift für Physik”，63，1930）。直接实验重建这幅肖像需要精确测量时间分辨荧光光谱，对非共振频率和描述光子产生的超快动力学具有高灵敏度。在这项工作中，我们展示了这样的实验技术在超导波导量子电动力学（wQED）平台，使用单个transmon量子比特和两个耦合transmon量子比特作为量子发射器。在这两种情况下，光子肖像同意定量与输入输出理论的预测和定性与维格纳-Weisskopf理论。我们相信，我们的技术不仅允许有趣的可视化的基本原理，但可以作为一种工具，例如，实现多维光谱波导量子电动力学。
