Experimental Investigations On High Dimensional Entanglement And Plasmon Assisted Transmission

Quantum information science is a new field of science and technology, combining and drawing on the disciplines of physical science, mathematics, computer science, and engineering. Quantum entanglement is one of the most important subject, and also, the strangest part of quantum information, it is the foundation of quantum teleportation, quantum computation, quantum cryptography, superdense coding, etc.In recent years, the interest in high dimensional entangled states, or qudits, is steadily growing because entangled qudits have some advantages over entangled qubits. One advantage of using multilevel systems is its promise to realize new types of quantum communication protocols, and its better properties in quantum cryptography than qubits. These cryptography protocols are more robust against specific classes of eavesdropping attacks. The other advantage is their possible implementation in the fundamental tests of quantum mechanics. For two-partite system of dimension greater than two, it has been found that the Clauser-Horne-Shimony-Holt(CHSH) inequality can be maximally violated, and this violation continues to survive in the limit of infinite dimensions.The experiments showing plasmon-assisted transmission of entangled photons in polarization and in energy-time also have attracted a lot of interest. The reason is that large systems are more prone to decoherence processes, and, therefore, entanglement should be a very fragile property for them. The plasmons involve a mesoscopic number of electrons of about 10¹⁰. These experiments demonstrated that plasmons do carry collectively only a single degree of freedom, i.e., a single qubit. Apart from its fundamental significance, this effect may provide another platform to transfer entanglement between photons and condensed-matter materials for storing, modulating, and even engineering quantum information with subwavelength metal optics. These works combine two fields of research, namely quantum information and nano-structured metal optics.In this dissertation, we mainly focus on the investigation of high dimensional entangled states and surface plasmon-assisted transmission. The works are listed as follows:1.High dimensional spatial modes entanglement in spontaneous parametric down conversionWe calculate the relative amplitude of orbital angular momentum (OAM) and Hermite-Gaussian mode entangled photon pairs from the spontaneous parametric down conversion of a thin quadratic nonlinear crystal. These entanglements occur in infinite dimensional Hilbert space and can be used in the investigation of high dimensional entangled systems. We also...