Study In The Spectral Properties Of The Coincident-frequency Entangled Photon Source

Time is a fundamental physical quantity which is currently the most accurate.Precision time not only in the field of basic research is important, also there arewidely used in applied research, national defense and national economy. Theapplication of chronometer time is inseparable from the high precision timesynchronization technology. The accuracy of traditional time synchronization islimited by the shot noise limit in the classic measurement. In order to make themeasurement accuracy break through the shot noise limit, the concept of quantumtime synchronization is proposed. In the state of an ideal photon number squeezingand coincident-frequency entanglement, the accurate degree of measuring the signalpulse propagation delay will reach quantum mechanics Heisenberg limit---sub-picosecond and even femtosecond.The frequency-entangled source as a time signal carrier is widely used inquantum time synchronization technology. Therefore, the characteristics of quantumentanglement source directly affect the final accuracy of the synchronization. Thegeneration and fully understand of high quality frequency-entangled resources play akey role in the quantum clock synchronization systems.In this paper, we analyze the frequency-entangled resource generated fromspontaneous parametric down-conversion. The main contents and results of the studyare as follow:(1).we have characterized the time relevant properties of frequency entangledbiphoton source before, now we characterized the frequency relevant properties fordifferent pump and calculated the degree of entanglement. This experience resultsprovide theory basis for analyzing the relationship between the degree of frequencyentanglement and the accuracy of quantum time synchronization.(2).The experience results are compared with the theoretical results，Verify theeffects of different the laser bandwidth on a frequency-consistent entanglementproperties of the light source;(3).We construct experience system based on optical fiber link. In the HOMinterferometer quantum time synchronization protocol, we achieved long distancetransmission of entangled two-photon and locked two arms of HOM interferometer equaling. We also measured the effect of temperature on fiber length.