Collective enhancement of quantum coherence in coupled quantum dot films

Colloidal semiconductor quantum dots (QDs) are attractive materials that provide unique photophysics of multiple electron-hole pairs (multiexcitons) in strongly quantum confined systems. Multiexciton phenomena such as efficient Auger recombination have been intensively investigated with respect to individual QDs. However, the cooperative nature of QDs, especially in terms of multiexciton coherence, has not been elucidated thus far. Here, we report the observation of the collective enhancement of quantum coherence in coupled QD films. Using a photocurrent quantum interference technique, we find that the multiexciton quantum coherence in coupled QDs is significantly increased compared to the case of isolated QDs. This cooperative effect is induced by the coherent electronic coupling between QDs. Our results clarify the enhancement mechanism in coupled quantum systems and open the door to advanced optoelectronic applications such as coherent amplifiers and frequency upconverters.