Accessing the dark exciton with light
Accessing the dark exciton with light
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DOI：
10.1038/nphys1812
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发表时间：
2010-12-01
期刊：
影响因子：
19.6
通讯作者：
Gershoni, D.
中科院分区：
文献类型：
--
作者：
Poem, E.;Kodriano, Y.;Gershoni, D.
半导体中的基本光激发是具有反平行自旋的电子-空穴对：“亮”激子。光学活性直接带隙半导体及其纳米结构中的亮激子已被深入研究。在量子点中，明亮的激子提供了光与相互作用的受限电荷载流子的自旋之间的重要界面。最近，在这些纳米结构中的单个电子和空穴的自旋状态的完全控制已经被证明，这是使用这些两能级系统进行量子信息处理的必要步骤。原则上，亮激子的自旋也可以直接用作二能级系统。然而，由于其短的辐射寿命，其用途是有限的。具有平行自旋的电子-空穴对形成长寿命的、光学不活跃的“暗激子”，并且由于它大多被认为是不可接近的激发而受到较少的关注。在这项工作中，我们证明了暗激子形成了一个相干的两级系统，可以很容易地被外部光访问。我们证明：将其自旋态光学制备为两个本征态的相干叠加，在由其本征态之间的能量差限定的频率下进行其自旋态的相干旋进，以及通过电荷添加和随后的偏振光子检测来读出自旋。
The fundamental optical excitation in semiconductors is an electron-hole pair with antiparallel spins: the 'bright' exciton. Bright excitons in optically active, direct-bandgap semiconductors and their nanostructures have been thoroughly studied. In quantum dots, bright excitons provide an essential interface between light and the spins of interacting confined charge carriers. Recently, complete control of the spin state of single electrons and holes in these nanostructures has been demonstrated, a necessary step towards quantum information processing with these two-level systems. In principle, the bright exciton's spin could also be used directly as a two-level system. However, because of its short radiative lifetime, its usefulness is limited. An electron-hole pair with parallel spins forms a long-lived, optically inactive 'dark exciton', and has received less attention as it is mostly regarded as an inaccessible excitation. In this work we demonstrate that the dark exciton forms a coherent two-level system that can fairly easily be accessed by external light. We demonstrate: optical preparation of its spin state as a coherent superposition of two eigenstates, coherent precession of its spin state at a frequency defined by the energy difference between its eigenstates, and readout of the spin by charge addition and subsequent polarized photon detection.