Excitation dynamics in a three-quantum dot system driven by optical near-field interaction: towards a nanometric photonic device.

Using density operator formalism, we discuss interdot excitation energy transfer dynamics driven by the optical near-field and phonon bath reservoir, as well as coherent excitation dynamics of a quantum dot system. As an effective interaction between quantum dots induced by the optical near-field, the projection operator method gives a renormalized dipole interaction, which is expressed as a sum of the Yukawa functions and is used as the optical near-field coupling of quantum dots. We examine one- and two-exciton dynamics of a three-quantum dot system suggesting a nanometric photonic switch, and numerically obtain a transfer time comparable with the recent experimental results for CuCl quantum dots.

Demonstrating nanophotonic switching using near-field pump-probe photoluminescence spectroscopy of CuCl quantum cubes.

We demonstrated a novel optical switching operation using three CuCl quantum cubes with a size ratio of. Their quantized excitonic energy levels resonate with one another, and the switching mechanism was based on the resonant near-field energy transfer between the quantum cubes. Using near-field pump-probe photoluminescence spectroscopy, we succeeded in controlling the near-field energy transfer and obtained a controlled (i.e. switched) signal in a differential photoluminescence spectrum with and without a pump beam. The internal quantum efficiency of the switching operation was close to 1. These results suggest the possibility of making a nanophotonic switching device smaller than 30 nm.

Optical near fields as photon-matter interacting systems.

A quantum theoretical formulation of an optical near-field system developed using the projection operator method is shown to be applicable to conventional problems in the optical near field in a unified way, and also addresses different quantum mechanical issues such as atom manipulation and nano-fabrication. To gain a clear insight, the effective mass of exciton-polarizations is introduced; this depends on the sizes of the probe tip and sample. We calculate the optical near-field intensity detected by (a) a probe sphere and (b) tapered probe modelled by two spheres. The results show that the size of the probe tip determines the spatial resolution, while the contribution of the tapered part causes degradation of the signal contrast. A size-resonance effect between the probe and sample is predicted. Furthermore, enhancement of the signal intensity is observed at the edges of a circular aperture perpendicular to incident polarization. These results are consistent with those obtained from different methods. The approach employed is shown to be a valuable tool in physical understanding and analysis of the near-field optical phenomena as well as experimental situations.