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Journal of Shaanxi Normal University

The quantum measurement of the distant clock synchronization

Yongfang Li

Published Jan 1, 2009• 0 citations
OpenAlex

Abstract

Based on the quantum feature and the quantum coherent principle of the entangled photon pairs produced with the spontaneous parametric down-conversion,a measurement method of the distant clock synchronization is studied.This method can not only be used in studying the distant clock synchronization and the quantum positioning,but is useful in measuring the time difference of a pair of entangled photon passing the nonlinear crystal.The results show that the shorter the time difference is,the better the coherence and synchronization of the two probed events are.

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Based on the quantum feature and the quantum coherent principle of the entangled photon pairs produced with the spontaneous parametric down-conversion,a measurement method of the distant clock synchronization is studied.This method can not only be used in studying the distant clock synchronization and the quantum positioning,but is useful in measuring the time difference of a pair of entangled photon passing the nonlinear crystal.The results show that the shorter the time difference is,the better the coherence and synchronization of the two probed events are.
The time synchronization accuracy on the order of nanoseconds can be provided using the conventional methods of time synchronization,a higher measurement accuracy on the order of femto-seconds can be reached by quantum measurement which employs entangled photon pairs in order to break the limit of measurement accuracy of conventional methods.The second-order correlation function of the entangled photon pairs which produced in a spontaneous type?Ⅱparametric down-conversion is investigated by integral transforming in the nonlinear crystal and substituting the first order expand of the wave vector.The relation between the second-order correlation function and temporal difference.A quantum method in clock synchronization between satellite and ground station is proposed based on the temporal correlation.The simulation indicates that the measurement accuracy provided by the second-order correlation function can be 70femto-seconds and the synchronization accuracy in the scheme can be 140femto-seconds in the ideal case.
Photon pairs generated in spontaneous parametric downconversion exhibit a strong correlation in time, which has been used to synchronize spatially separated clocks in the past in quantum key distribution implementations to a high accuracy. A symmetric version of this scheme can be used to allow for an absolute clock synchronization, and the entanglement properties of photons generated in spontaneous down conversion allows to strengthen the authenticity of the received signals through entanglement witnesses. Aspects of this time synchronization technique with respect to use in optical fibers and remaining vulnerabilities are discussed. [1] C. Ho, A. Lamas-Linares, and C. Kurtsiefer: Clock synchronization by remote detection of correlated photon pairs, New Journal of Physics 11, 045011 (2009). [2] J. Lee, L. Shen, A. Cerè, J. Troupe, A. Lamas-Linares, C. Kurtsiefer: Symmetrical clock synchronization with time-correlated photon pairs, Appl. Phys. Lett. 114, 101102 (2019).
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.
We present an algorithm for synchronizing two clocks based on second‐order quantum interference between entangled photons generated by parametric down‐conversion. The procedure is distinct from the standard Einstein two‐way clock synchronization method in that photon correlations are used to define simultaneous events in the frame of reference of a Hong‐Ou‐Mandel (HOM) interferometer. Once the HOM interferometer is balanced, by use of an adjustable optical delay in one arm, arrival times of simultaneously generated photons are recorded by each clock. Classical information on the arrival times is sent from one clock to the other, and a correlation of arrival times is done to determine the clock offset.
The synchronization of distant clocks is of considerable importance for many practical and scientific applications. The new protocol for clock synchronization based on quantum theory is proposed in this paper. The experiment framework mostly same as Mach-Zehnder interferometer. We can determine the time difference through exchange of each other's photons .The main features of this scheme is of need not transfer a real hardware clock or measure any time during the synchronization. Compare with classical methods, this protocol is not limited by any dispersion and gravitational potential that maybe present in the propagation. So the ping-pong protocol can achieve more precision than classical methods. The new one's precision is related with the number of circulation in the experimentation.