Classical and quantum based information transfer and dissemination in space communication

Charles H. Bennett

Qi Shen, Jian-Yu Guan, Ting Zeng +15 more

Time and frequency transfer lies at the heart of the field of metrology. Compared to current microwave dissemination such as GPS, optical domain dissemination can provide more than one order of magnitude in terms of higher accuracy, which allows for many applications such as the redefinition of the second, tests of general relativity and fundamental quantum physics, precision navigation and quantum communication. Although optical frequency transfer has been demonstrated over thousand kilometers fiber lines, intercontinental time comparison and synchronization still requires satellite free space optical time and frequency transfer. Quite a few pioneering free space optical time and frequency experiments have been implemented at the distance of tens kilometers at ground level. However, there exists no detailed analysis or ground test to prove the feasibility of satellite-based optical time-frequency transfer. Here, we analyze the possibility of this system and then provide the first-step ground test with high channel loss. We demonstrate the optical frequency transfer with an instability of $10^{-18}$ level in 8,000 seconds across a 16-km free space channel with a loss of up to 70~dB, which is comparable with the loss of a satellite-ground link at medium earth orbit (MEO) and geostationary earth orbit (GEO).

F.J. Duarte, T S Taylor

Isabella Dumé

Physicists have transferred time and frequency information over more than 100 km in free space, far exceeding previous records.

Kera Carter

Josef Vojtěch, Tomáš Novák, Elisabeth Andriantsarazo +16 more

With the increasing demand for ultra-precise time synchronization and frequency dissemination across various scientific, industrial, and communication fields, the Czech Republic has developed an innovative, non-commercial fiber-based infrastructure. This infrastructure serves as a shared platform, utilizing optical fibers to enable high-precision timing, coherent frequency transfer, and a newly implemented vibrational sensing capability. The project also addresses challenges posed by classical communication noise—particularly from Raman scattering—on quantum channels, especially for Quantum Key Distribution (QKD). By strategically separating classical and quantum channels into distinct wavelength bands, such as the C-band and O-band, the infrastructure achieves minimal interference while enabling multiple concurrent applications over shared fiber lines.