“The Optical Activity of the Dark Exciton and its Potential Use for Generating a Cluster State of Entangled Photons”

The dark exciton in semiconductors is formed when an electron is promoted from the full valence band to the empty conduction band and, in addition, its spin projection is flipped. Since light does not interact with the electronic spin, in general, this excitation is not expected to decay radiatively, and therefore, it is termed a dark exciton. In practice, however, we discovered experimentally that, in semiconductor quantum dots, the dark exciton does have optical activity, and it can be optically accessed and coherently controlled. I will present a simple model which explains this optical activity in terms of the reduced symmetry of a typical self-assembled semiconductor quantum dot. In addition, I will present a detailed model in which the quantum dot-confined dark exciton is used as an entangler for generating a string of entangled photons, or a photonic cluster state. In order to accomplish this much desired feat with high fidelity, it is crucial to be able to model the physical processes involved precisely. I will discuss a model and simulations of the temporal evolution of a one-dimensional photonic cluster state produced by a sequence of optical pulses applied to a quantum dot with a dark exciton in it, using Lindblad dynamics. My model will be favorably compared with recent experimental results.