Macroscopic coherence of a single exciton state in a polydiacetylene   organic quantum wire
  We show that a single exciton state in an individual ordered conjugated polymer chain exhibits macroscopic quantum spatial coherence reaching tens of microns, limited by the chain length. The spatial coherence of the k=0 exciton state is demonstrated by selecting two spatially separated emitting regions of the chain and observing their interference. 
F. Dubin, R. Melet, T. Barisien, R. Grousson, L. Legrand,, M. Schott &   V. Voliotis