title: Demonstration of quantum synchronization based on second-order quantum coherence of entangled photons.
abstract: Based on the second-order quantum interference between frequency entangled photons that are generated by parametric down conversion, a quantum strategic algorithm for synchronizing two spatially separated clocks has been recently presented. In the reference frame of a Hong-Ou-Mandel (HOM) interferometer, photon correlations are used to define simultaneous events. Once the HOM interferometer is balanced by use of an adjustable optical delay in one arm, arrival times of simulta- neously generated photons are recorded by each clock. The clock offset is determined by correlation measurement of the recorded arrival times. Utilizing this algorithm, we demonstrate a proof-of-principle experiment for synchronizing two clocks separated by 4 km fiber link. A minimum timing stability of 0.44 ps at averaging time of 16000 s is achieved with an absolute time accuracy of 73.2 ps. The timing stability is verified to be limited by the correlation measurement device and ideally can be better than 10 fs. Such results shine a light to the application of quantum clock synchronization in the real high-accuracy timing system.
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Runai
authors.initials: R
authors.lastname: Quan
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Yiwei
authors.initials: Y
authors.lastname: Zhai
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Wang
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Feiyan
authors.initials: F
authors.lastname: Hou
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Shaofeng
authors.initials: S
authors.lastname: Wang
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Xiang
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Liu
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.
authors.forename: Shougang
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi'an, 710600, China.
authors.forename: Ruifang
authors.initials: R
authors.lastname: Dong