Spin Noise Spectroscopy on Zero-Dimensional Semiconductor Nanostructures

本方案的主要内容是利用自旋噪声谱对单量子点中重空穴的自旋动力学进行全面的研究。这种量子光学技术在过去的十年中已经发展成为一种非常通用和强大的工具，用于研究半导体纳米结构中的自旋和电荷动力学。它特别适合于研究平衡和非平衡条件下的单个局域自旋，以探索剩余的挑战，因为它在自旋-光子接口和量子信息技术中的潜在应用。在第一步中，我们将通过零差检测对自旋噪声信号进行光学放大来提高测量灵敏度。自旋噪声的光学放大已经在原理验证实验中被成功地证明，并且可以将所需的测量时间减少几个数量级。对单个正电荷量子点的自旋噪声测量得到了固有的纵向空穴-自旋弛豫时间和横向空穴-自旋退相干时间。自旋弛豫时间将被测量为外加纵向磁场的函数，特别关注30mT到2T之间的中等磁场区域，这一区域到目前为止还没有被实验很好地研究。理论研究表明，自旋弛豫时间受双声子过程控制，在此范围内有一个极大值。作为晶格温度函数的磁场相关的自旋弛豫时间的额外测量可以证实或证伪这一理论。由于应变引起的重空穴-轻空穴混合和复杂的超精细相互作用，我们发现常用的(InGa)As量子点的自旋退相干时间比自旋弛豫时间要短得多。使用一种新型的几乎无应变的GaAs量子点与横向外加磁场相结合，可以实现更长的自旋相干时间。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所决定。为了更深入地了解载流子-核自旋相互作用，我们将研究更高阶的自旋噪声关联。与通常在自旋噪声光谱中研究的二阶自旋相关谱不同，四阶相关谱可以揭示超精细相互作用的各向异性，这与所研究的量子点中的重空穴-轻空穴混合量有关。

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.