| High-precision time signals are widely used in national life,scientific research,po-litical economy and other fields.High-precision time synchronization technology enables high-precision time signals to be widely used.In order to transmit the time signal with high fidelity,the accuracy of the time trans-fer means must be higher than the accuracy of the time signal being transmitted.The two-way time transfer method is a highly accurate time synchronization method.In the process of the two-way time transfer,since the signals are simultaneously transmitted in the same path in converse directions,the asymmetry of the transmission path is physically overcomed.According to different transmission paths,there are two-way satellite time frequency transfer（TWSTFT）,time transfer by laser link（T2L2）and two-way optical fiber time transfer（TWOFTT）.In recent years,the accuracy of atomic clocks has reached 10-19level.The existing time transfer technology can not meet the accuracy requirements of the time-frequency signal transmission between the optical frequency atomic clocks of 10-19level.It is ur-gent to study and develop new long-distance high-precision time transfer methods and techniques.At the beginning of the 21st century,scientists proposed the concept of quantum time synchronization.Exploiting quantum techniques,which utilize quantum squeezed or entangled sources and quantum measurement technology,the ultimate shot noise limit to the classical time-of-arrival measurement precision can be broken through,thus much better timing stability is expected.In this paper,a high-power 780 nm laser generated by external cavity frequency doubling pumped type-II phase-matched PPKTP crystal and an efficient 1560nm fre-quency anti-correlated entanglement source was obtained.On this basis,combining the advantages of two-way time transfer and quantum time synchronization,we proposed the fiber-based two-way quantum time synchronization protocol for the first time,and studied the protocol theoretically and experimentally.The research contents and results are as follows:（1）We studied the generation and quantum properties of the communication band anti-correlated frequency entangled source of 1560 nm.In order to generate an efficient frequency anti-correlated entanglement source,a high-power narrow-line width fiber laser was used as the source,and a high-power 780 nm laser was generated as a pump source af-ter frequency doubling in the external cavity,after single pass through the type-II PPKTP crystal a frequency anti-correlated entanglement source of 1560 nm was finally obtained.The single photon count of the entangled source was 370 kHz,the coincidence count was22 kHz,the frequency indistinguishability was 95±3%,the center wavelengths of the signal and idle photons were 1560.23±0.03 nm and 1560.04±0.03 nm respectively,and the bandwidth was 3.22±0.01 nm.The band width of two photon coincidence was0.52 nm and the entanglement degree was 6.19.The brightness of the entangled source is sufficient to be transmitted in an optical fiber of several tens of kilometers,we generated high efficiency frequency entangled source for subsequent quantum time synchronization experiments.（2）The two-way quantum time synchronization protocol was theoretically proposed and experimentally demonstrated.In the experiment,the traditional time correlation measurement instrument was replaced by the combination of event timers and data post-processing,and the remote clock synchronization demonstration was realized.And the characteristics of nonlocal dispersion cancellation were demonstrated by non-local mea-surements.Two-way time synchronization experiment was carried out on a 20-km fiber coiling,time synchronization stability was 0.922±0.004 ps@5 s,0.045±0.038 ps@40960s.In order to evaluate the stability of the experimental system,we measured the time synchronization stability when no transmitting fiber was inserted,and obtained the time stability of 0.450±0.001 ps@5 s,0.030±0.014 ps@40960 s.By measuring the relation-ship between the average time offset and the length of the transmitting fiber,we obtained the absolute time accuracy of the experimental system was 1.23 ps. |
