Observation of Faraday rotation from a single quantum-dot spin

Here, we present an all-optical dispersive measurement of a single spin confined in a self-assembled InAs/GaAs quantum dot (QD) (Atature etl., 2007). The time-averaged spin-state is observed via spin-dependent Faraday rotation of a spectrally detuned laser, induced by the polarization-and spin-selective trion transitions. The measurement was performed with a spin prepared by an independent laser (Atature et al., 2006) and in the case of a thermal state.