Spin Noise Spectroscopy on Zero-Dimensional Semiconductor Nanostructures

• Applicant: Professor Dr. Michael Oestreich
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2015 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268295520

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.

• DFG Programme: Research Grants
• International Connection: Russia
• Cooperation Partners: Professor Dr. Fei Ding; Professor Dr. Mikhail Glazov, until 3/2022; Professor Dr. Daniel Hägele