Raman coherence beats from the entangled state involving polarized excitons in single quantum dots

The optically induced and detected entangled state involving an exciton Zeeman doublet with entanglement entropy as high as $\sim 0.7$ was created using picosecond lasers in single $\mathrm{GaAs}$ quantum dots. The temporal evolution of the nonradiative Raman coherence between two exciton states was directly resolved in quantum beats measured in the homodyne detected differential transmission experiment. The Raman coherence time, $66\pm 15\mathrm{ps}$, was determined from the decay of the envelope of the quantum beats, and was found to be limited by the lifetimes of the exciton transitions, $50\pm 3\mathrm{ps}$.