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arXiv:quant-ph/0407204 · Applied Physics Letters

Distant clock synchronization using entangled photon pairs

Alejandra Valencia, Giuliano Scarcelli, Yanhua H. Shih

Published Sep 27, 2004• 179 citations
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Abstract

We report a proof-of-principle experiment on distant clock synchronization. Besides the achievement of picosecond resolution at 3km distance, this experiment demonstrated a concept for high-accuracy nonlocal timing and positioning based on the quantum feature of entangled states.
DOI
10.1063/1.1797561

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In quantum communication experiments using entangled photon pairs far-distant measurement results are correlated on the sub-nanosecond level. For best performances the timing of the coincidence window and its width are critical. In contrast to lab experiments, where accurate timing could be adjusted easily by e.g. matched cable length, in distributed experiments a common clock more accurate than the coincidence time is requested by means of time stable synchronization channels or atom clocks synchronized by GPS. Synchronization of distant clocks is far from trivial. Efficient synchronization mechanisms are required to enable novel architectures like switched star shaped QKD-networks and facilitate quantum communication of a high number of potential users.
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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 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.