Preparation And Application Of Correlated-photon Pairs Based On Guided Wave System

With the rapid development of quantum optics in recent years,great progress has been made in single photon infrared detection technology,quantum key distribution,cold atom quantum information storage,vector light field regulation,quantum computing simulator and other fields.Therefore,quantum light source has gradually become a hot research topic.It has become an important research content to obtain the associated photon pairs with high purity,easy collection and high preparation efficiency.The photon pair produced by Spontaneous Parameter Down Conversion(SPDC)has the advantages of simple structure,few required components,high photon pair brightness and high signal-to-noise ratio.However,the line width of the associated photon pair obtained by this method is relatively wide,which is difficult to meet the application requirements of narrowband light source in quantum storage and quantum measurement.In order to solve this problem,Fiber Based Fabry-Perot Cavity(FFPC)is constructed by coating both ends of SPDC crystal.The influence of temperature on the gain curve of SPDC crystal is studied theoretically,and the generation condition of narrow line-width correlation photon pair is obtained.The application of correlated photon pairs in precise measurement of optical fiber length and entanglement of photon orbital angular momentum is explored.Firstly,the influence of temperature on the gain curve of SPDC is studied based on the analysis of the influence of one-way loss factor of resonator on the line width of resonator light wave mode and the stability conditions of different kinds of resonators,and the temperature to achieve the optimal phase matching condition is determined.It is proved that the stable output of single longitudinal mode,high purity and narrow linewidth associated photon pairs can be achieved by preparing F-P microcavity with specific coated nonlinear crystals.Secondly,a new method for precise measurement of optical fiber length based on the matched electric retarder with associated photon pairs is proposed.Based on the optical fiber length measurement system composed of electric retarder,superconducting nanowire single-photon detector and time coincidence measuring device,the optical fiber length was accurately measured by comparing the shift of optical signal coincidence peak position before and after the optical fiber was connected to the optical path by adjusting the delay amount of signal optical path electrical retarder DG535.The measurement results of different lengths of optical fibers show that the measurement system has the advantages of high precision,adjustable measurement range and strong robustness.Finally,the application of correlated photon pairs in the preparation of entangled photon orbital angular momentum states is studied.On the basis of constructing a declarative photon source with nonlinear crystal,the entanglement of photons with different orbital angular momentum degrees of freedom is realized by q-plate.The fidelity coefficient of entangled photon is 95.84%,which proves that the declarative light source can be used as high quality entangled light source.