Optical Spin Noise of a Single Hole Spin Localized in an (InGa)As Quantum Dot

We advance spin noise spectroscopy to the ultimate limit of single spin detection. This technique enables the measurement of the spin dynamic of a single heavy hole localized in a flat (InGa)As quantum dot. Magnetic field and light intensity dependent studies reveal even at low magnetic fields a strong magnetic field dependence of the longitudinal heavy hole spin relaxation time with an extremely long $T_1$ of $\ge 180\mu \mathrm{s}$ at 31 mT and 5 K. The wavelength dependence of the spin noise power discloses for finite light intensities an inhomogeneous single quantum dot spin noise spectrum which is explained by charge fluctuations in the direct neighborhood of the quantum dot. The charge fluctuations are corroborated by the distinct intensity dependence of the effective spin relaxation rate.

Figure 1

The solid black and red lines show the PL spectrum for two orthogonal linear polarizations (${\pi }^x$, ${\pi }^y$). The blue squares depict the measured integrated spin noise power ($P_{\mathrm{SN}}$) which corresponds to the $T_1$ spin noise. The inset shows a typical spin noise spectrum at $B_z=31\mathrm{mT}$ after only 12 minutes integration time.

Figure 2

Dependence of the spin relaxation rate of the Lorentzian spin noise spectrum on the longitudinal magnetic field. The black squares show the saturation of the linewidth at constant probe laser intensity due to optical QD excitation. The red dots depict the linewidth corrected to the lowest possible probe intensity. The red line is a fit to the intensity corrected linewidths with $B^{-\alpha }$ and $\alpha =3/2_{-0.04}^{+0.08}$.

Figure 3

Spin relaxation rate versus probe laser intensity at constant detuning. The deviation from a linear relation between ${\mathrm{\Gamma }}_1$ and probe laser intensity reveals that the single QD has not a single resonance but experiences sustained step-like charge fluctuations in its vicinity. The red line is a fit according to Eq. (1) (see [40] for the fitting parameters).