Spin noise of electrons and holes in self-assembled (In,Ga)As quantum dots

We measure the frequency spectra of random spin fluctuations, or ``spin noise", in ensembles of (In,Ga)As/GaAs quantum dots (QDs) at low temperatures [1]. We employ a spin noise spectrometer based on a sensitive optical Faraday rotation magnetometer that is coupled to a digitizer and field-programmable gate array, to measure and average noise spectra from 0-1 GHz continuously in real time (no experimental dead time) with sub-nanoradian/$\sqrt{\textrm{Hz}}$ sensitivity. Both electron \emph{and} hole spin fluctuations generate distinct noise peaks, whose shift and broadening with magnetic field directly reveal their \emph{g}-factors and dephasing rates within the ensemble. A large, energy-dependent anisotropy of the in-plane hole \emph{g}-factor is clearly exposed, reflecting systematic variations in the average QD confinement potential. [1] arXiv:0909.1592