Virtual photonic couplings of quantum nanostructures

Electric interactions among charges is one of the fundamental aspects of physics, and have a long research history, arriving the common understanding that they are the results of interchanges of photons between charges [1]. However, it has been retarded to directly introduce this photon exchange scheme into physics of solids, mainly because the range of the mediating photon was not long enough to cover the distance of usual concerns, e.g. size of devices in conventional integrated circuits. However, this retardation should be lifted not just to improve our understanding, but to refine our nanotechnology on the basis of what is really happening in the nanostructures. Therefore, we have first focused on dipole-dipole interaction, especially the resonance dynamic dipole- dipole interaction (RDDDI) among transition dipoles, publishing on the generation of an intrinsic nonlinear localized mode as early as 1996, and subsequently on quantum gate application with quantum dots (QDs), coherent modes in an ensemble of QDs, a parity conserving dynamic Förster type mechanism between identical tuned QDs involving a real photon (RPH) or virtual photon (VPH), and the RDDDI mechanism between nonidentical detuned realistic GaAs QDs assisted by VPHs showing fine structures in photoluminescence (PL) spectra [2]. Our data are taken on each QD individually, see Fig.1, whereas other published data were so far measured on ensembles of QDs, e.g. solution-grown statistical number of CdSe QDs collected in a layered structure [3]. Our VPH assistance model gives direct and clear image for the interaction of nonidentical QDs, differing from thus far proposed theoretical schemes of the Förster energy transfer in solids. In this paper, first, the RDDDI between a pair of QDs of different sizes under moderate excitation power is described theoretically including the VPHs and parity inheritance. Then a typical micro-PL spectrum of the individual QD pair is presented, demonstrating the postulate that the pair of 0.3 meV split peaks are the result of the intermittent swiching between coupling and noncoupling. Furthermore, we illustrate more general resonance dynamic multipole-multipole interactions (RDMMIs) by plotting the interaction energy and range as a function of inter-polar distance, see Fig. 2 [4]. This RDMMI should inevitably appear in the course of realizing quantum information devices such as quantum computer in the near future.