Eliminating the confined dark-exciton qubit precession using an externally applied magnetic field

We investigate experimentally and theoretically the behavior of the confined dark exciton in an InAs/GaAs semiconductor quantum dot, under the application of an external magnetic field in a Voigt configuration. We show that by varying the magnitude and direction of the external field one can accurately control the dark-exciton fine-structure splitting. In addition, we show that the dark-exciton spin state is approximately polarized along the cubic crystallographic directions [100] or equivalents. By comparing our experimental results with a model for the exchange and Zeeman interactions, we find the conditions for nullifying the fine-structure splitting between the two eigenstates of the dark exciton, thereby stopping its qubit precession.