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Realization of Sub-picosecond Clock Synchronization based on Second-Order Quantum Coherence

Runai Quan, Ruifang Dong, Yiwei Zhai, Mengmeng Wang, Shaofeng Wang, Feiyan Hou, Tao Liu, Shougang Zhang

Published Jan 1, 2015• 1 citation
Publisher

Abstract

Based on the second-order quantum interference between entangled photons generated by parametric down conversion, we have demonstrated a proof-of-principle experiment of synchronizing two clocks separated by 4-km fiber link. A sub-picosecond accuracy is achieved.
DOI
10.1364/cleo_qels.2015.ftu2a.2

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Quantum clock synchronization schemes utilizing frequency-entangled pulses have flourished for their potentially superior precision to the classical protocols. In this Letter, a new experimental record based on the second-order quantum interference algorithm is reported, to the best of our knowledge. The synchronization accuracy between two parties separated by a 6 km fiber coiling link, which is evaluated by the time offset shift relative to that with the fibers removed, has been measured to be 13±1 ps. The stability in terms of time deviation (TDEV) of 0.81 ps at an averaging time of 100 s has been achieved. The long-term synchronization stability is seen determined by the measurement device, and a minimum stability of 60 fs has been reached at 25,600 s. Furthermore, for the first time to the best of our knowledge, we quantify the performance of this quantum synchronization scheme, and very good agreements with the experimental results have been achieved. According to the quantum simulation, further improvements for both the synchronizing stability and accuracy can be expected.
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.