Reconfigurable Photon Sources On Silicon Photonic Chip

Quantum computation shows great advantages compared with classical computing due to its quantum characters such as superposition and entanglement.Optical quantum computing system is considered to be a promising candidate because its advantages of long coherent time,easy for coding and manipulating,easy to connect with quantum communication system.And on-chip optical quantum computing is believed to be more practical compared with the bulk optical scheme because of the better integration,stability,scalability and reconfigurability.Among the various integrated platforms for optical quantum computing,silicon-based photonic chips have become a promising choise because the CMOS-compatible technology,large nonlinear coefficient and high intergration.According to the practical requirements of silicon-base optical quantum computing,in this thesis we study the quality of the on-chip optical quantum bit systematically,including photon purity,brightness,wavelength tunablility and multiple sources.The main research contents are as follows:1.We propose a new phase matching method for silicon waveguide chips,the evanescent wave coupling phase matching,and realize a widely wavelength tunable photon source based on two coupled waveguides.Numerical simulation and calculation methods are used to verify the tunability.By modulating the coupling coefficient between the coupled waveguides,the wavelength's tuning range of entangled photons can reach more than 1000 nm.It is a general phase matching method and can be extended to any third-order or second-order nonlinear material system.2.We propose a high spectral purity photon source based on interferometer coupled microring.We design and fabricate such microring structures with different parameters on a single silicon chip,and verify the purity by spectral correlation measurement and second-order autocorrelation measurement.A high spectral purity of95% ± 1.5% is obtained which is higher than other schemes reported.Such high spectral purity source can be used to realize high visibility quantum interference and improve the fidelity of on-chip quantum computing.3.We propose and implement a multi-purpose tunable photon source.By designing a microring coupled by cascaded Mach-Zehnder interferometers,we can tune the two adjustable phase-shifters to control the quality factors of the pump,signal and idler independently.Experimently we fabricate such a microring chip and find it can be tuned to achieve the best four wave mixing efficiency conditions,the best generation rate condition and the best purity condition.The multi-degree adjustable microring chip can meet the requirements of many applications in quantum optics and nonlinear optics.4.We also study multiple single photon sources and propose a high quality four photon source on a silicon chip.Based on the dual Mach-Zehnder interferometer coupled microring,a four photon source with high brightness,high purity,high indistinguishability and high stability is produced by pumping the same microring in two directions.We have tested the spectral purity and the correlation characteristics of two-photon spectrum,and verify the indistinguishability of four photons by on-chip Mach-Zehnder interference experiment.The on-chip high quality four photon source can effectively expand the computing scale of the optical quantum chip and lay the foundation for the preparation of more photons and the realization of quantum algorithm.