Generation And Manipulation Of Entangled Photons Based On Counterpropagating Quasi-Phase-Matching

Quantum information science is a comprehensive subject combining quantum physics,computer science and information science.The photon system is one of the most important systems to realize quantum information technologies due to the advantages including robustness of decoherence,easy manipulation,relatively simple preparation.Moreover,photons are the natural flying qubits,which plays an indispensable role in quantum communication.Entangled photons are the core resource of the applications of photonic quantum information technologies,and play an important role in the research of quantum physics fundamentals as well.The efficient generation and manipulation of entangled photons is a hot topic in international research.Non-linear optics(NLO)is a common way to generate and manipulate entangled photons.One of the NLO branches is the second-order NLO effects,including spontaneous parametric down-conversion for generating entangled photon pairs,electro-optic effect to control the photon phase and polarization,and the sum and difference frequency effects for realizing photon frequency conversion,bandwidth compression,spectrum analysis,and time-resolved detection,etc.The NLO processes based on quasi-phase-matching in optical superlattices have the virtues of flexible matching wavelengths,high efficiency,and function integration.Further combining the waveguide technology,it can realize multi-functional integrated active photonic chips.This dissertation makes research on the realization of counterpropagating phase matching via the quasi-phase-matching technique,as well as the applications in generation and manipulation of entangled photons.Counterpropagating phase matching has the advantages of narrow phase-matching bandwidth and natural separation of entangled photons.It can produce entangled photons with distinguished features such as narrow bandwidth and frequency decorrelation.In the applications of photon frequency conversion,it can further compress the spectrum bandwidth.This dissertation mainly includes the following contents:1.The introduction chapter introduces the research background,related concepts and research progress,including quantum information science,second-order nonlinear optical effects,quasi-phase matching and the optical superlattices.2.The second chapter introduces the basic concepts and characteristics of counterpropagating phase matching,and reviews several realization methods.Then the spectral properties of counterpropagating phase matching are theoretically analyzed,and the generation of photon pairs with narrowband and frequency decorrelation is calculated and discussed3.In chapter 3,an experimental realization of narrowband polarization entanglement source based on counterpropagating quasi-phase matching is presented.The narrow-band polarization-entangled photon pairs are produced from a periodicallypoled potassium titanate(PPKTP)waveguide with a period of 1.3 micron which is pumped simultaneously on both ends of the waveguide.The bandwidth of the entangled photons are accurately measured to be 7.1 GHz by spectrum measurement and Hong-Ou-Mandel interference,respectively.The brightness,fidelity and entanglement property of the entangled photon source are characterized.The entangled photon source bandwidth can match the solid-state quantum memory bandwidth well,thus showing potential applications in long-distance quantum communication and quantum repeaters.4.The fourth chapter presents a theoretical scheme for frequency conversion and bandwidth compression via counterpropagating quasi-phase-matching process.The experimental scheme based on PP lithium niobate on insulator is presented with optimized bandwidth compression by the design of waveguide dispersion.The compression ratio and the peak power of the pump for 100% conversion are calculated.The scheme can be used to realize quantum communication interface,so as to meet the requirements of different photon wavelengths.