Effect of inter-dot distance on excitonic dephasing in quantum dot chains

We present a study of the dephasing of an excitonic qubit trapped within a chain of two semiconductor quantum dots immersed in a bulk material. We consider a specific excitonic wave-function which spreads across the chain. The source of the dephasing is the phonon field of the bulk material interacting with the single exciton within the structure. We show that an excitonic wave function which extends over more than one quantum dot is remarkably more robust against the dephasing. The details of dephasing depends on the distance which separates the two quantum dots. In particular, as this distance increases, the residual coherence increases up to a maximum value. However, the short-time dephasing is shown to be characterised by the appearance of a transient behavior. The actual duration of this transient is determined by the separation between the dots.