The Quantum Interference Of Surface Plasmon Polaritons

With the rapid development of science and technology, people are requiring a much faster speed of information processing. However, bottlenecks are appearing in the development of classical information technology. Quantum information technology began to attract people’s attention for studying. To be practical, integration has become a necessary for quantum information. However, the traditional optical devices could not break through the optical diffraction limit, which limits their application in quantum photonic integrated circuits. Therefore, the surface plasmons, electron-density waves which can break the diffraction limit and propagate in subwavelength, began to be used in the quantum photonic integrated circuits.Due to its smaller size than conventional optical waveguide, surface plasmons waveguide is suitable for integration, and has attracted more and more people on the research of surface plasmons. It becomes a promising way for using surface plasmons as information carrier in quantum photonic integrated circuits. At the meanwhile, it’s also a very interesting and promising research of designing functional devices in quantum photonic integrated circuits based on the properties of the surface plasmons.In this paper, surface plasmons waveguide is fabricated by nano-fabrication technology, and its application in quantum information is also studied. This thesis included three parts as listed in the following:1. Preparation of dielectric-loaded surface plasmon waveguide and the basically study of its properties.Dielectric-loaded surface plasmon polariton waveguide is considered as a waveguide structure with the best performance in several common surface plasmon waveguides. Because this kind of waveguide ensure a good trade-off between the effective transmission distance in the waveguide and the confinement of waveguide mode.The structure of dielectric-loaded surface plasmon polariton waveguide is a PMMA (an electron-beam photoresist) waveguide which is on top of Au film, means that this kind of waveguide can be fabricated by electron beam lithography. By improving our fabrication technology, we are able to fabricate this subwavelength waveguide according to our requirements, and use it in our experiment.A fiber tapered is used to near-field excite surface plasmon polaritons in the dielectric loaded waveguide, which is theoretically considered as a very effective way. We achieved the surface plasmon polaritons’ excitation in the waveguide by the fiber taper in the experiment, and observed the scattered light signals from the surface plasmon polaritons at the end of the waveguide.2. The quantum interference of single surface plasmons.Quantum interference is an important way for the quantum operation of photons. It is an important question for that whether the quantum interference can be demonstrated by surface plasmons, if we use the surface plasmon as an information carrier in quantum integrated photonic circuit.We observed a quantum interference with a very high visibility of single surface plasmon polaritons in experiment. This proves the boson nature of the single surface plasmon polariton. And this also suggests that single plasmons can be used as qubits to carry quantum information and achieve on-chip linear optical computations or quantum simulations.The loss effect of surface plasmon polaritons on the quantum interference have also been discussed. Our discussion reveals that loss can change the second-order quantum-interference visibility. In addition to reducing the absorption loss, special attention should be paid when designing photonic circuits for a quantum-information process.3. The design of integrated functional device based on multi-mode dielectric-loaded surface plasmon polariton waveguide.Compared to traditional photonic waveguide which is a single-mode waveguide, multimode dielectric loaded surface plasmon polariton waveguide can be used to design the devices which is compactable and functional.We design a directional coupler structure based on multi-mode dielectric-loaded surface plasmon polariton waveguide, which can separate different modes in the waveguide. With the help of this kind of directional coupler, we can encode information in different modes.We also find that the splitting ratio of this kind of directional coupler can be adjusted without changing its size, and we observed the variation of splitting ratio in experiment.