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Scientific Reports

Quantum two-way time transfer with different wavelengths

Alejandro Rodriguez Perez, Anouar Rahmouni, Thomas Gerrits, Cordell Mazzetti, Nicolas Makovnik, Harry C. Shaw, Eleanya E. Onuma, Richard L. Slonaker, La Vida Cooper

Published Sep 3, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1038/s41598-026-68305-z

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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.
Abstract Quantum clock synchronization (QCS) can measure out the high-precision clock difference among distant users, which breaks through the standard quantum limit by employing the properties of quantum entanglement. Currently, the wavelength division multiplexed QCS network has been demonstrated with a spontaneous parametric down-conversion entangled photon source. In this paper, we propose a more efficient QCS network scheme with the wavelength multicasting entangled photon source, which can decrease at least 25% of wavelength channel consumption under the identical network scale. Afterwards, a four node QCS network is demonstrated, where the wavelength multicasting entangled photon source is utilized with dual-pumped four-wave mixing silicon chip. The experimental results show that the measured time deviation is 3.4 ps with an average time of 640 s via the multiple fiber links of more than 10 km.
The two-way quantum time transfer method has been proposed and experimentally demonstrated for its potential enhancements in precision and better guarantee of security. To further testify its advantage in practical applications, the applicable direct transmission distance as well as the achievable synchronization precision between independent time scales is of great interest. In this paper, an experiment on two-way quantum time transfer has been carried out over a 50 km long fiber link. With the common clock reference, a short-term stability of 2.6 ps at an averaging time of 7 s and a long-term stability of 54.6 fs at 57300 s were obtained. With independent clock references, assisted by microwave frequency transfer technology, the achieved synchronization showed almost equal performance and reached a stability of 89.5 fs at 57300 s. Furthermore, the spectral consistency of the utilized entangled photon pair sources has been studied concerning its effect on the transfer accuracy and long-term stability. The results obtained have promised a bright future of the two-way quantum time transfer for realizing high-precision time synchronization on metropolitan area fiber links.
High-precision time transfer is of fundamental interest in physics and metrology. Quantum time transfer technologies that use frequency-entangled pulses and their coincidence detection have been proposed, offering potential enhancements in precision and better guarantees of security. In this paper, we describe a fiber-optic two-way quantum time transfer experiment. Using quantum nonlocal dispersion cancellation, time transfer over a 20-km fiber link achieves a time deviation of 922 fs over 5 s and 45 fs over 40 960 s. The time transfer accuracy as a function of fiber lengths from 15 m to 20 km is also investigated, and an uncertainty of 2.46 ps in standard deviation is observed. In comparison with its classical counterparts, the fiber-optic two-way quantum time transfer setup shows appreciable improvement, and further enhancements could be obtained by using new event timers with subpicosecond precision and single-photon detectors with lower timing jitter for optimized coincidence detection. Combined with its security advantages, the femtosecond-scale two-way quantum time transfer is expected to have numerous applications in high-precision middle-haul synchronization systems.
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.
Based on frequency entangled sources and arrival time measurements, a best time synchronization stability result of fewer than 100 fs has been reported over 20km fiber links, verifying the superiority of quantum time synchronization. In this paper, a two-way quantum time transfer over 50 km fiber links with the same frequency standard was implemented, with a short-term stability of 2.63 ps at an averaging time of 18 s and a long-term stability of 79.2 fs at 73700 s. The system accuracy in terms of the 50km fiber transfer length is measured as 524.75 ps, the agreement of which with the theoretical simulation illustrates that improving the spectral consistency of the two entangled sources will significantly improve the accuracy. This result shows that the fiber-optic two-way quantum time transfer can be successfully extended to a metropolitan fiber link distance of around 50 km or longer, not only maintaining the transfer stability well below picosecond but also promising further improvements in synchronization accuracy.
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.