Synchronizing clocks across the planet with femtosecond accuracy could become reality by applying a laser frequency comb technique recently developed at NIST. The team tested their technique by beaming frequency comb pulses between mountains on two islands in Hawai‘i, demonstrating the fidelity necessary to link clocks via satellite even if the signal is very weak. The team’s method, which could make synchronization of distant clocks 10,000 times more accurate than we can currently achieve, might contribute to testing general relativity, redefining the second to an optical standard, and future searches for dark matter.
Credit: B. Hayes/NIST
Last year, scientists drove up Mauna Loa volcano on Hawai‘i, aimed a laser at a reflector positioned on Haleakala peak on Maui, and beamed rapid pulses of laser light through 150 kilometers of turbulent air. While the pulses were exceedingly faint, they demonstrated a capability long sought by physicists: transmitting extremely precise time signals through the air between far-flung locations at powers that are compatible with future space-based missions.
The results, obtained by a team including scientists from the National Institute of Standards and Technology (NIST), could enable time transfer from the ground to satellites 36,000 kilometers away in geosynchronous orbit, where they hang stationary above a point on the Earth’s surface. The method would permit this time synchronization with femtosecond precision — 10,000 times better than the existing state-of-the-art satellite approaches. It also would allow for successful synchronization using the bare minimum timing signal strength, which would make the system highly robust in the face of atmospheric disturbances.
Coordinating arrays of distant devices to this substantially higher degree offers several intriguing possibilities. While state-of-the-art optical atomic clocks are extraordinarily precise, comparing clocks that are separated by continents requires a signaling method that can convey that preci ..
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