Optimization Of Portable Frequency Entanglement Sources And Measurement Of Their Quantum Properties

Due to strong frequency correlation and time correlation,frequency entanglement sources are widely used in the field of quantum precision measurement,such as quantum time synchronization and quantum positioning.At present,with the development of quantum time synchronization and other fields in China,the loss of frequency entanglement sources in long distance transmission links and the portability of outdoor experiments have to be taken into consideration when conducting experimental research in related fields.This puts forward a new requirement for frequency entanglement source,that is,one needs a portable and transportable entanglement source with high single photon number and high coincidence count.However,the existing sources of frequency entanglement in China cannot satisfy the requirements of modern quantum time synchronization experiments.Therefore,it is very necessary to develop a portable frequency entanglement source with the above advantages.In this paper,the optimization and quantum characteristics measurement were carried out based on the existing frequency entanglement source in the Quantum Time Synchronization Laboratory of National Time Service Center,Chinese Academy of Sciences.The main content includes four parts:The first part(Chapter 2)introduces the theory of frequency entanglement sources,including the common generation methods and characterization methods of frequency entanglement sources;In the second part(Chapter 3),the optimization process of the PPLN waveguide is introduced in detal,including the structure,optical path design,technical details and parameters of the optimized entanglement source,etc.In addition,the stability and reliability of the optimized entanglement source are also evaluated.In the third part(Chapter 4),the quantum properties of the optimized frequency entanglement source are measured in terms of single photon counting,coincidence counting,entanglement degree,HOM interference,the violation of energy-time inequality,etc.In the fourth part(Chapter 5),an experimental method is proposed to quickly measure the phase-matched wavelength of entangled photons as a function of crystal temperature.This method can be used to calibrate the relationship between phase-matched wavelength and crystal temperature and the poling period,and it is expected to modify or improve the temperature-dependent Sellmeier equation.The optimized portable frequency entanglement source is superior in the evaluation of single-photon counts,coincidence counts,stability,portability and related quantum performance,therefore providing a reliable portable frequency entanglement source and related technical support for quantum time synchronization experiments in outdoor long-distance transmission links.