Three-Band Quantum Coherences in Semiconductors: Theory and Experiment

尽管在原子和分子三能级系统中，许多重要的非线性相干光学效应，如电磁诱导透明、无反转激光、暗态和绝热布居转移等已经得到很好的证实，但在半导体中发现类似效应的潜力还没有被开发。这项研究的目的是将这些原子/分子物理技术应用于凝聚态系统的研究。具体地说，将对半导体量子阱中的激子三带相干进行实验和理论研究。主要目的是识别激子三能带系统和原子三能级系统之间的相似和根本区别。在实验上，这项工作是基于飞秒双色激光脉冲，分别耦合到重洞激子和轻洞激子。理论分析包括对辐射和非辐射量子相干、能带结构效应和量子力学多体关联的描述。所考虑的非线性相干效应和基本物理问题是：(I)激子三带拉比振荡，(Ii)半导体中的相干暗态，(Iii)重空穴到轻空穴的绝热布居转移，以及(Iv)电荷-载流子关联对这些效应的影响，例如价带间电荷-载流子散射，激子-激子散射，以及双激子效应。这项研究将与研究生一起进行，他们将因此获得凝聚态物理和材料科学前沿领域的研究技能。这些技能将使他们成为21世纪技术劳动力中富有成效的成员。*在原子中，激光通常不是简单地被吸收，而是导致电子的相干和可逆激发。在最简单也可能是最基本的情况下，光诱导了一种由原子中电子的激发和去激发组成的振荡行为。另一方面，半导体倾向于简单地吸收光，不允许这种连贯和可逆的过程。然而，最近的实验表明，在超短时间尺度上，半导体确实表现出一定的相干效应，这与它们的原子同行有一些相似之处。在这个项目中，我们试图通过使用超短光脉冲的实验和允许对半导体进行量子力学描述的理论相结合，来观察和建立一些半导体-原子的类比。我们关注涉及两个耦合电子跃迁的半导体系统，因为与这些系统对应的原子，即所谓的三能级原子，在非线性光学和激光物理中具有深远的应用前景。这些研究的结果对推动半导体在技术设备中的开发和使用具有巨大的潜力。这项研究涉及研究生，他们将接受当代凝聚态物理和材料科学的前沿领域之一的培训。这项培训将使他们成为21世纪技术劳动力中富有成效的成员。%

Whereas in atomic and molecular three-level systems a number of important nonlinear coherent optical effects, such as electromagnetically-induced transparency, lasing without inversion, dark states, and adiabatic population transfer are by now well established, the potential of finding analogous effects in semiconductors has not yet been exploited. The purpose of this research is the application of these techniques of atomic/molecular physics to the study of condensed matter systems. Specifically, experimental and theoretical studies will be performed of excitonic three-band coherences in semiconductor quantum wells. The main goal is the identification of similarities and fundamental differences between excitonic three-band systems on the one hand and their atomic three-level counterparts on the other hand. Experimentally, the work is based on femtosecond two-color laser pulses, which couple to the heavy-hole and the light-hole exciton, respectively. The theoretical analysis includes the description of radiative and non-radiative quantum coherences, bandstructure effects, and quantum mechanical many-body correlations. The nonlinear coherent effects and basic physical issues under consideration are (i) excitonic three-band Rabi oscillations, (ii) coherent dark states in semiconductors, (iii) adiabatic heavy-hole-to-light-hole population transfer, and (iv) the influence of charge-carrier correlations on these effects, for example intervalence-band charge-carrier scattering, exciton-exciton scattering, and biexcitonic effects. This research will be conducted with graduate students who will thereby acquire research skills in a forefront area of condensed matter physics and materials science. These skills will enable them to be productive members of the technical workforce of the 21st century.***In atoms, laser light is usually not simply absorbed, but leads to coherent and reversible excitations of electrons. In the simplest and probably most fundamental scenario, the light induces an oscillatory behavior that consists of excitation and de-excitation of the electrons in the atom. Semiconductors, on the other hand, tend to simply absorb light, not allowing for such coherent and reversible processes. However, recent experiments have shown that, on ultrashort timescales, semiconductors do exhibit certain coherent effects, which bear some resemblance to their atomic counterparts. In this project, we try to observe and establish some of these semiconductor-atom analogies through a combination of experiments with ultrashort light pulses and a theory that allows for a quantum mechanical description of semiconductors. We focus on semiconductor systems that involve two coupled electronic transitions, because the atomic counterpart to these systems, the so-called three-level atoms, promise far-reaching applications in nonlinear optics and laser physics. The results of these investigations have great potential to advance the development and use of semiconductors in technological devices. This research involves graduate students who will receive training in one of the forefront areas of contemporary condensed matter physics and materials science. This training will prepare them to be productive members of the technological workforce of the 21st Century.%%%