Abstract

The read-out of a single confined electron spin trapped in a quantum dot constitutes a milestone for solid-state quantum information processing. While Faraday rotation measurements have been performed on semiconductor spin ensembles, single-shot spin read-out has only been achieved using transport measurements. Here, we present an all-optical dispersive measurement of a single spin confined in a self-assembled InAs/GaAs quantum dot (QD) [1]. 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 [2] and in the case of a thermal state. We estimate that within a detection timescale, on the order of 10 measurement-induced spin-flips occur. If this number can be reduced well below unity, it will enable us to perform back-action evading spin measurements, or single-shot spin readout, which then will provide the means to resolve natural QD spin dynamics revealing spin quantum jumps. This seems within reach with the help of technical improvements such as application of solid-immersion lenses and commercial high-responsivity detectors, without the need for a cavity.

© 2007 IEEE