%0 Journal Article %T Electric-field-induced coherent coupling of the exciton states in a single quantum dot %A A. J. Bennett %A M. A. Pooley %A R. M. Stevenson %A M. B. Ward %A R. B. Patel %A A. Boyer de la Giroday %A N. Sk£żld %A I. Farrer %A C. A. Nicoll %A D. A. Ritchie %A A. J. Shields %J Physics %D 2012 %I arXiv %R 10.1038/nphys1780 %X The signature of coherent coupling between two quantum states is an anticrossing in their energies as one is swept through the other. In single semiconductor quantum dots containing an electron-hole pair the eigenstates form a two-level system that can be used to demonstrate quantum effects in the solid state, but in all previous work these states were independent. Here we describe a technique to control the energetic splitting of these states using a vertical electric field, facilitating the observation of coherent coupling between them. Near the minimum splitting the eigenstates rotate in the plane of the sample, being orientated at 45{\deg} when the splitting is smallest. Using this system we show direct control over the exciton states in one quantum dot, leading to the generation of entangled photon pairs. %U http://arxiv.org/abs/1203.5909v1