We demonstrate that high-dimensionality coherent spectroscopy yields “super-resolved” spectra whereby peaks may be localized far below their homogeneous line width by resolving them across multiple, coherently coupled dimensions. We implement this technique using a fifth-order photon-echo spectroscopy called Gradient-Assisted Multidimensional Electronic–Raman Spectroscopy (GAMERS) that combines resonant and nonresonant excitation to disperse the optical response across three spectral dimensions: two involving excitonic transitions and one that encodes phonon energies. In analogy to super-resolution localization microscopies, which separate spatially overlapping signals in time, GAMERS isolates signals spectrally using combined electronic and nuclear resolution. Optical phonon lines in a colloidal solution of CdSe quantum dots at room temperature separated by less than 150 μeV are resolved despite the homogeneous line width of these transitions being nearly an order of magnitude broader. The frequency difference between these phonon modes is attributed to softening of the longitudinal phonon mode upon excitation to the lowest exciton state. Further, such phonon mode selectivity yields spectra with electronic line widths that approach the single particle limit. Through this enhanced spectral resolution, the GAMERS method yields insights into the nature of coupling between longitudinal optical and acoustic phonons and specific excitonic transitions that were previously hidden.

中文翻译：

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单颗粒均匀线宽以下的量子点的激子-声子光谱

我们证明，高维相干光谱会产生“超分辨”光谱，其中峰可以通过跨多个相干耦合的维度进行解析而定位在远低于其均一线宽的位置。我们使用称为梯度辅助多维电子拉曼光谱（GAMERS）的五阶光子回波光谱技术来实现此技术，该技术结合了共振和非共振激发，将光学响应分散在三个光谱维度上：两个涉及激子跃迁，一个编码声子。能量。类似于将时间上重叠在空间上重叠的信号的超分辨率定位显微图像类似，GAMERS使用组合的电子和核分辨率在频谱上隔离了信号。在CdSe量子点的胶体溶液中，在室温下相隔小于150μeV的光子声子线得以分辨，尽管这些跃迁的均匀线宽几乎宽了一个数量级。这些声子模之间的频率差归因于在激发到最低激子状态时纵向声子模的软化。此外，这种声子模式选择性产生具有接近单个粒子极限的电子线宽的光谱。通过这种增强的光谱分辨率，GAMERS方法可以洞悉纵向光学声子与声子之间的耦合性质以及以前隐藏的特定激子跃迁。