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.
Highlights
Time transfer over 158 km long optical link with minimum value of 300 fs in terms of time deviation (TDEV) at averaging time of 10 s has been presented[37]
Experimental implementation focusing on the quantum clock synchronization is few, except that a one-way synchronization of clocks was reported by Valencia group[51], which accomplished an experimental demonstration at 3 km fiber distance with an accuracy of picosecond
We report a proof-of-principle experiment on synchronizing two clocks separated by 4-km fiber link based on HOM quantum interference between two frequency entangled photons
Summary
Time transfer over 158 km long optical link with minimum value of 300 fs in terms of time deviation (TDEV) at averaging time of 10 s has been presented[37]. In contrast to classical synchronization schemes, the accuracy of this protocol is independent of knowledge of their relative locations or the properties of the intervening medium Based on this idea, a general framework[45] as well as several multiparty clock synchronization protocols[46,47] were further proposed. By accurate control of an optical delay line and on the resolution of second order quantum interference exhibited by correlated photons in a HOM interferometer[56], a sub-picosecond or even lower timing stability could be achieved Based on this algorithm, a long-term synchronizing stability of 0.44 picosecond is achieved, which is mainly limited by the performance of the time-arrivals correlation measurement device and can in principles reaches the level of a few femtoseconds. By improving the generation and detection efficiency of the frequency entangled photon pairs in the experimental scheme, it may find important applications in radio astronomy, such as in VLBI
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