Spin Noise Spectroscopy on Zero-Dimensional Semiconductor Nanostructures

本文的主要课题是利用自旋噪声光谱对单量子点的重空穴自旋动力学进行综合研究。这种量子光学技术在过去十年中已经发展成为研究半导体纳米结构中自旋和电荷动力学的一种非常通用和强大的工具。它特别适合于研究平衡和非平衡条件下的单定域自旋，以探索自旋光子界面和量子信息技术中潜在应用的剩余挑战。在第一步，我们将通过纯差检测对自旋噪声信号进行光学放大，以提高测量灵敏度。自旋噪声的光学放大已经在一个原理验证实验中得到了成功的证明，并且可以将所需的测量时间减少几个数量级。在单个带正电的量子点上测量自旋噪声，得到纵向空穴自旋弛豫时间和横向空穴自旋退相干时间。自旋弛豫时间将作为一个外部纵向磁场的函数来测量，特别关注在30mT和2T之间的中等磁场区域，迄今为止还没有得到很好的实验研究。理论研究表明，自旋弛豫时间受双声子过程的支配，并在该状态下有最大值。对磁场相关的自旋弛豫时间作为晶格温度的函数的额外测量可以证实或证伪这一理论。由于应变诱导的重孔光孔混合和由此产生的复杂超精细相互作用，发现常用的（InGa）As量子点中的自旋退相干时间明显短于自旋弛豫时间。使用一种新型的几乎无应变的砷化镓量子点与横向外磁场相结合，更长的自旋相干时间应该是可行的。我们将测量几乎无应变的GaAs量子点中的自旋退相干时间作为横向磁场的函数，并将其与应变（InGa） as量子点中的自旋退相干时间进行比较。在没有外加磁场的情况下，自旋弛豫和退相干时间主要由空穴自旋与核自旋的超精细相互作用决定。为了更深入地了解载流子-核自旋相互作用，我们将研究高阶自旋噪声相关。与自旋噪声光谱中常用的二阶自旋相关谱相比，四阶相关谱可以揭示超精细相互作用的各向异性，这与所研究量子点中重空穴光空穴混合的数量有关。

The main topic of the present proposal is the comprehensive investigation of the heavy-hole spin dynamics in single quantum dots using spin noise spectroscopy. This quantum optical technique has evolved during the last decade into an extremely versatile and powerful tool to study the spin and charge dynamics in semiconductor nanostructures. It is particularly suitable for studying single localized spins under equilibrium as well as non-equilibrium conditions in order to explore the remaining challenges in view of potential applications in spin-photon interfacing and quantum information technologies in general. In a first step, we will improve the measurement sensitivity by optical amplification of the spin noise signal via homodyne detection. The optical amplification of spin noise has already been demonstrated successfully in a proof-of-principle experiment and can reduce the required measurement time by orders of magnitude.The spin noise measurements on a single positively charged quantum dot yield the intrinsic longitudinal hole-spin relaxation time as well as the transverse hole-spin decoherence time. The spin relaxation time will be measured as a function of an external longitudinal magnetic field with special focus on the regime of moderate magnetic fields between 30mT and 2T which is so far not well investigated by experiments. Theoretical studies suggest that the spin relaxation time is governed by two-phonon processes and has a maximum value in this regime. Additional measurements of the magnetic-field-dependent spin relaxation time as a function of the lattice temperature can confirm or falsify this theory. The spin decoherence time in the commonly-used (InGa)As quantum dots was found to be significantly shorter compared to the spin relaxation time in consequence of strain-induced heavy-hole light-hole mixing and the resulting complex hyperfine interaction. Longer spin coherence times should be feasible using a new type of virtually strain-free GaAs quantum dots in combination with a transverse external magnetic field. We will measure the spin decoherence time in the virtually strain-free GaAs quantum dots as a function of the transverse magnetic field and compare it to the spin decoherence time in the strained (InGa)As quantum dots. In the absence of external magnetic fields, the spin relaxation and decoherence times are dominated by the hyperfine interaction of the hole spin with the nuclear spins. To gain more insight into the carrier-nuclear spin interaction, we will study spin noise correlations of higher order. In contrast to the second-order spin correlation spectrum commonly studied in spin noise spectroscopy, a fourth-order correlation spectrum can reveal inter alia the anisotropy of the hyperfine interaction, which is associated with the amount of heavy-hole light-hole mixing in the investigated quantum dot.