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arXiv:2009.04815 · Optics Express

Absolute clock synchronization with a single time-correlated photon pair source over a 10 km optical fibre

Jianwei Lee, Lijiong Shen, Adrian Nugraha Utama, Christian Kurtsiefer

Published May 2, 2022• 16 citations
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Abstract

We demonstrate a point-to-point clock synchronization protocol based on bidirectionally propagating photons generated in a single spontaneous parametric down-conversion (SPDC) source. Tight timing correlations between photon pairs are used to determine the single and round-trip times measured by two separate clocks, providing sufficient information for distance-independent absolute synchronization secure against symmetric delay attacks. We show that the coincidence signature useful for determining the round-trip time of a synchronization channel, established using a 10 km telecommunications fiber, can be derived from photons reflected off the end face of the fiber without additional optics. Our technique allows the synchronization of multiple clocks with a single reference clock co-located with the source, without requiring additional pair sources, in a client-server configuration suitable for synchronizing a network of clocks.

DOI
10.1364/oe.455542

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We demonstrate a point-to-point clock synchronization protocol based on bidirectionally propagating photons generated in a single spontaneous parametric down-conversion (SPDC) source. Tight timing correlations between photon pairs are used to determine the single and round-trip times measured by two separate clocks, providing sufficient information for distance-independent absolute synchronization secure against symmetric delay attacks. We show that the coincidence signature useful for determining the round-trip time of a synchronization channel, established using a 10 km telecommunications fiber, can be derived from photons reflected off the end face of the fiber without additional optics. Our technique allows the synchronization of multiple clocks with a single reference clock co-located with the source, without requiring additional pair sources, in a client-server configuration suitable for synchronizing a network of clocks.
We demonstrate a point-to-point clock synchronization protocol based on bidirectionally exchanging photons produced in spontaneous parametric down conversion. The technique exploits tight timing correlations between photon pairs to achieve a precision of 51 ps in 100 s with count rates of order 200 s−1. The protocol is distance independent, is secure against symmetric delay attacks, and provides a natural complement to techniques based on Global Navigation Satellite Systems. The protocol works with mobile parties and can be augmented to provide authentication of the timing signal via a Bell inequality check.
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).
Abstract The quantum entanglement distribution network, serviced as the communication infrastructure which distributes quantum information among remote users, enables many applications beyond the reach of classical networks. Recently, the applications such as quantum key distribution and quantum secure direct communication, have been successfully demonstrated in the quantum entanglement distribution network. In this article, we propose a multi-user round-trip quantum clock synchronization (QCS) scheme in the quantum network, which can be implemented with one single entangled photon source located at the server. The server distributes the entangled photons to remote multiple users with the wavelength division multiplexing strategy, and each user feeds partial received photons back to the server. The clock difference between the server and each user is calculated from the one-way and round-trip propagation times, which are determined according to the time correlation of entangled photons. Afterwards, the demonstration has been conducted between the server and a user over a 75-km-long fiber link, where the measured clock difference uncertainty is 4.45 ps, and the time deviation is 426 fs with an average time of 4000 s. Furthermore, the proposed QCS scheme is linearly scalable to many users, with respect to user hardware and number of deployed fibers.
Quantum networking, distributed quantum sensing and computing, financial markets, and position navigation and timing of satellites, require high precision clock synchronization. Existing quantum two-way time transfer protocols rely on identical wavelengths at each location. In this letter we derive and experimentally validate a heterogeneous wavelength quantum two-way time transfer protocol that eliminates the need for matched entangled-photon sources. The difference in propagation time is explicitly accounted for by incorporating the group refractive index to the calculations. Using a custom-built spontaneous parametric down-conversion photon-pair source, we separate signal and idler with wavelength division multiplexing, while maintaining strong frequency anti-correlation between signal and idler. We show that the dispersion effects on the second-order correlation function can be removed with the addition of dispersion compensation fiber. We performed quantum time transfer between two independent atomic clocks separated by a 15 km fiber spool with a time deviation of 658 fs at 0.2 s averaging time and 3.9 ps at 1 s averaging time. These results demonstrate a pathway for high precision time transfer in heterogeneous networks.