Semiconductor nanocrystals, commonly known as colloidal quantum dots (QDs), have revolutionized the field of quantum physics. These nanocrystals exhibit size-dependent colors that directly illustrate the quantum size effect. While physicists had an understanding of size-dependent quantum effects, the actual realization of these effects into tangible nanoscale objects was only made possible through the discovery of QDs.
Researchers worldwide are actively exploring the potential of QDs in studying quantum effects and phenomena. These nanocrystals serve as a material platform for investigating phenomena such as single-photon emission and quantum coherence manipulation. One significant challenge in studying quantum effects is the direct observation of Floquet states, which are instrumental in explaining coherent interactions between light fields and matter.
A recent study published in Nature Photonics by Prof. Wu Kaifeng and his team from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences achieved a groundbreaking milestone in observing Floquet states in semiconductors. Unlike previous studies conducted in low-temperature, high-vacuum environments, this study implemented all-optical spectroscopy in the visible to near-infrared region under ambient conditions.
The researchers utilized quasi-two-dimensional colloidal nanoplatelets with atomically precise quantum confinement in the thickness dimension. This unique structure enables interband and intersubband transitions in the visible and near-infrared regions, forming a three-level system. Through the interaction of visible and near-infrared photons, the researchers were able to observe the transition of Floquet states in real-time.
One of the key findings of the study was the dephasing of the Floquet state into real population within hundreds of femtoseconds. This observation challenges the assumption that Floquet states dissipate outside the temporal overlap of pump and probe pulses. The experimental results were further validated through quantum mechanical simulations, providing a comprehensive understanding of the dynamics of Floquet states in semiconductors.
Prof. Wu emphasized the significance of this study in unlocking the spectral and dynamic physics of Floquet states. By demonstrating the observation of Floquet states in semiconductor materials under ambient conditions, the study paves the way for utilizing Floquet engineering in controlling optical responses and coherent evolution in condensed-matter systems. This advancement opens up new possibilities for manipulating surface/interfacial chemical reactions through nonresonant light fields, expanding the scope of quantum engineering in solid-state materials.
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