Functional operations using a near-field optically coupled quantum-dot system

We investigate the population dynamics in a three quantum-dot system coupled via an optical near field, which consists of a coherent operation part and an output part. We analytically show that a resonance condition between the two parts depends on initial excitation in the coherent operation part. Using this feature, AND- and XOR-gate operations are demonstrated in the case of symmetrically arranged quantum dots. We also evaluate the effects of asymmetric arrangement on these operations, and show that the coherence plays an important role in an asymmetric system.