Entangled photons serve as an important tool in the field of quantum information processing. Traditionally, spontaneous parametric down-conversion (SPDC) in second-order nonlinear crystals has been the workhorse source for generating entangled photons. However, those SPDC-generated photons are notoriously difficult to couple into single-mode optical fibers due to mode mismatch, thus limiting their use in potentially realizable fiber-optic quantum networks. Fiber-based entanglement sources provide an elegant solution to the coupling problem by directly producing entangled photons in an optical fiber. The fundamental parametric process invoked is called four-wave mixing (FWM), wherein a pair of entangled photons (called signal and idler) is created at the expense of two pump photons. In this thesis, classical aspects of FWM are reviewed, which serve as the basis for our quantum mechanical theory of FWM-generated two-photon state. Various extensions of the above theory have been formulated, including the theories of filter-shape-dependent two-photon state, polarization-entangled two-photon state, and degenerate-frequency two-photon state. Temporally correlated photons are generated using two different kinds of fiber --- microstructure fiber and dispersion-shifted fiber. A purity metric of correlated-photon sources called CAR (coincidence to accidental ratio) is proposed and a theoretical CAR model is established, achieving qualitative agreement with experiment. Various methods are used to suppress spontaneous Raman scattering in optical fiber, which is the origin of uncorrelated noise photons. For generating polarization entangled photons, two schemes are described, namely, the Sagnac-loop scheme and the counter-propagating scheme. Each scheme's pros and cons are summarized. A double-loop scheme is then introduced, which is shown both theoretically and experimentally to have successfully combined the benefits of the two previous schemes. Indistinguishable photons are key resources needed in linear optical quantum computing. Correlated, as well as entangled, indistinguishable photons are successfully generated by using a co-polarized dual-frequency pump in a reverse degenerate four-wave mixing process. A novel 50/50 Sagnac-loop configuration is then introduced for generating spatially-separated identical photons, as well as its many other applications. Hong-Ou-Mandel interference, together with a quantum controlled-NOT gate, is demonstrated using this source. The use of a cross-polarized dual-frequency pump in generating identical photons is also investigated.

Last modified

• 05/30/2018

Creator

• Jun Chen

DOI

• https://doi.org/10.21985/N2FX30

Subject

• Electrical and Computer Engineering

Keyword

• quantum computation
• quantum splitter
• coincidence
• quantum communication
• entanglement
• nonlinear fiber optics

Date created

• 2007-05-14

Resource type

• Dissertation

Rights statement

• In Copyright