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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Indoor demonstration of free-space picosecond two-way time transfer on single photon level

Josef Blažej, Ivan Procházka, Jan Kodet, Pavel Linhart

Published Oct 3, 2014• 6 citations
Publisher

Abstract

The practical demonstration of an optical two-way time transfer based on single photon signal level has been completed. This approach enables to reach extreme timing stabilities and minimal systematic errors using existing electrooptic technologies. The crucial condition to almost eliminate systematic errors and to reach picosecond time transfer accuracy over free space communication channel is the maximum symmetry in experimental setup. In our indoor experiment we have achieved sub-picosecond precison and 3 ps accuracy. The entire system is compact and relatively simple.

DOI
10.1117/12.2062561

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The practical demonstration of an optical two-way time transfer based on single photon signal level has been completed. This approach enables to reach extreme timing stabilities and minimal systematic errors using existing electrooptic technologies. The crucial condition to almost eliminate systematic errors and to reach picosecond time transfer accuracy over free space communication channel is the maximum symmetry in experimental setup. In our indoor experiment we have achieved sub-picosecond precison and 3 ps accuracy. The entire system is compact and relatively simple.
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 remote clock synchronization is crucial for many classical and quantum network applications. Evaluating options for space-Earth links, we find that traditional solutions may not produce the desired synchronization for low Earth orbits and unnecessarily complicate quantum networking architectures. Demonstrating an alternative, we use commercial off-the-shelf quantum photon sources and detection equipment to synchronize two remote clocks across our free-space testbed utilizing a method called two-way quantum time transfer (QTT). We reach picosecond-scale timing precision under very lossy and noisy channel conditions representative of daytime space-Earth links and software-emulated satellite motion. This work demonstrates how QTT is potentially relevant for daytime space-Earth quantum networking and/or providing high-precision timing in GPS-denied environments.
High-precision time transfer over a long haul of fiber plays a significant role in many fields. The core method, namely cascading relay nodes for the compensation of signal attenuation and dispersion, is however insufficient to deal with crucial point-to-point transfer scenarios, such as harsh environments with extremely deficient infrastructure and emergency conditions. In long-distance signal transmission without any inline amplifiers, the high loss of the optical fiber link becomes the primary limiting factor, and direct use of traditional photodetectors at the receiving end will bring about a significant drop in the stability of detected signals. Here we propose a waveform-resolved single photon detection technique and experimentally perform tomography on the weak transferred signal with an average photon number of just 0.617 per pulse. By adopting this technique, we achieve the time deviation of 95.68 ps and 192.58 ps at 200 km and 300 km respectively at an averaging time of 1 s, overcoming the technical lower bound induced by traditional photodetectors. This work lays the foundation for through-type time transfer with high precision in those significant inline-amplification-free scenarios.
Fiber-optic Quantum clock synchronization has been proposed and experimentally demonstrated for its potential enhancements in precision and better guarantee of security. To further prove its advantage in practical applications, it is necessary to test its synchronization performance between clocks apart for at least intracity optical fiber distance. In this paper, we report a fiber-optic two-way quantum clock synchronization experiment with the distance reaching 50 km. With the common reference clock, a synchronization stability of 54.6 fs at 57300 s and an accuracy of 1.3 ps±36.6 ps have been achieved. With independent reference clocks, comparable performance has also been achieved combined with the microwave frequency transfer technology, which shows a stability of 89.5 fs at 57300 s. These results nicely showcase the feasibility of the two-way quantum clock synchronization to provide femtosecond-scale synchronization precision over intracity optical 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.