Logic and functional operations using a near-field optically coupled quantum-dot system

摘要

This paper investigates the exciton dynamics in a three-quantum-dot system coupled via an optical near field. The system consists of two identical quantum dots coupled coherently (the coherent operation part) and a third quantum dot with exciton sublevels (the output part). It provides certain characteristic functional operations depending on the initial excitation, as well as symmetry of the coupling strengths or the spatial arrangement. First, we analytically obtain the coupling strength between two quantum dots via an optical near field and give a numerical estimation for a CuCl quantum-cube system. Then, a resonance condition between the two parts is shown; this depends on the initial excitation in the coherent operation part. Using this condition, which can be realized by adjusting the energy level of a quantum dot in the output part, AND- and XOR-logic operations can be demonstrated in a symmetrically arranged quantum-dot system. We also discuss how the asymmetry of the system affects the energy transfer through certain coupled states in the coherent operation part that would be forbidden in a symmetrically arranged system. Although the asymmetry degrades the signal contrast for logic operations, it is expected to open up new techniques for novel device technologies where quantum entangled states are mediated in the operations.