ABSTRACT
The rapid advancement of integrated optoelectronics has been driven considerably by miniaturization. Following the path taken in electronics of reducing devices to their ultimately fundamental forms, for instance, single-electron transistors, now optical devices have also been scaled down, creating the increasingly active research fields of integrated nanophotonics.1-5 A fundamental nanophotonic device, involving single elementary excitations such as photons and spins, offers various advantages over a macroscopic object: its state can be controlled, initialized and read out with a precision at the fundamental quantum mechanical limit; its operational fidelity based on the interconversion of single excitations can approach 100%; and its functionality may be based on coherent rather than incoherent dynamics, allowing for devices that maintain quantum coherence, which is a crucial
requirement for applications in quantum information processing. Thus, a fundamental device could outperform traditional devices in terms of operation speed, integrability, and energy efficiency. On the fundamental level, a device consists of various coupled and/or integrated entities, such as single emitters, optical microresonators, optical waveguides, and photon-to-electron or photon-to-spin interfaces (Fig. 1.1). If different-material systems are involved (for example a combination of organic and inorganic units), then the resulting device might be appropriately described as “hybrid.” However, this term can also be used in a broader sense when new functionality is gained from a combination of different physical effects. Examples are the fusion of bioassays and micro-or nanoelectromechanical systems and that of microfluidics and optics. A merging of quantum optics and nanomechanics, photonics and atomic physics, or quantum optics and plasmonics is likely to provide new fundamental insight as well as novel applications such as quantum coherent devices or quantum-limited sensors.6-13 For example, a quantum computer, by contrast with its classical counterpart, needs to maintain coherent superpositions of discrete quantum states, acting as so-called quantum bits. A similar challenge occurs in quantum sensors, where exploitation of entangled quantum states allows for improved precision over classical equivalents. Whereas long storage times of quantum states may be possible, for example in atomic systems, fast read-out and information transfer using integrated optics, that is, an atomic-photonic hybrid system, would be desirable. The quantum mechanical decoherence and energy transfer processes in these hybrid systems are, however, not fully understood. This broader class of hybrid system is the motivation of this chapter, many of above applications will benefit from the understanding of the fundamental coupled integrated photonic system. This chapter emphasizes model systems combining metallic and dielectric nanophotonic constituents by scanning probe manipulation.A typical example of a hybrid nanophotonic system is photonic molecule. With the rapid progress of nanotechnology, many nanoscale photonic devices as small as 30 nm have been realized, which are very promising to achieve manipulation of photons at chip scale and having broad applications in renewable energy (photovoltaic cells, solid state lighting), telecommunications and bio medical
field.14,15 Recently, it was found that the electromagnetic modes of certain photonic devices are very similar to the electronic wave function of molecules16 (Figs. 1.2a-f). One of the most interesting examples is microresonators, especially when we arrange two or more microresonators together within optical coupling regime, the electromagnetic modes of the whole structure are very similar to the bonding (symmetric) or antibonding (antisymmetric) electronic wave function modes formed in molecules.17-20 It is interesting to study the photonic molecule of various structures using optical techniques and it may further improve our understanding of more complex photonic structures.
