How Scientists Built the World's Most Precise Timing Network
In the race to capture the most fleeting moments in the universe, scientists have built a timing system so precise it can measure a millionth of a millionth of a millionth of a second across distances longer than 30 city blocks.
Imagine trying to photograph a hummingbird's wings in perfect detail. Now imagine those wings flapping a quintillion times faster—that's the attosecond scale, where light travels less than the width of a single atom. At this unimaginably brief timescale, where one attosecond is to one second what one second is to the age of the universe, molecular and atomic processes unfold that were previously invisible to science.
For decades, capturing these processes remained beyond our grasp, not because we couldn't generate brief enough pulses of light, but because we couldn't synchronize equipment across large facilities with sufficient precision. That is, until researchers recently demonstrated a laser-microwave network that maintains attosecond timing precision across multi-kilometer distances for days at a time1 2 .
This breakthrough promises to revolutionize everything from drug development to materials science by allowing us to finally make "molecular movies" of processes like intramolecular charge transfer and Auger processes that alter chemistry at the attosecond level3 .
Before this breakthrough, the best synchronization available at large facilities like X-ray free-electron lasers (XFELs) was around 30 femtoseconds—30,000 times less precise than what attosecond timing offers.
These facilities often span kilometers and require dozens of optical and microwave sources to work in perfect synchrony for pump-probe experiments, where one laser pulse initiates a process and another probes it after a precisely controlled delay1 .
With attosecond synchronization, scientists will be able to observe phenomena that were previously only theoretical:
The researchers developed a sophisticated system that functions like a perfectly coordinated symphony, with each component playing a critical role in maintaining attosecond precision across a 4.7-kilometer network1 .
A mode-locked laser generates an extremely stable train of optical pulses with 216 MHz repetition rate and 170-femtosecond pulse width at 1550 nm wavelength.
The pulse train is sent through specialized fiber links to multiple end stations with active compensation for environmental disturbances.
Returning pulses are compared against fresh pulses using a balanced optical cross-correlator (BOC), detecting timing differences with attosecond sensitivity.
Error signals feed back to variable delay lines, continuously compensating for timing drifts and maintaining synchrony.
The experimental outcomes demonstrated unprecedented timing stability across various network configurations:
| Network Configuration | Distance | Timing Precision | Duration |
|---|---|---|---|
| Fiber network stabilization | 4.7 km | 580 attoseconds | Over 40 hours |
| Remote optical-optical synchronization | 3.5 km | 680 attoseconds | Over 40 hours |
| Complete laser-microwave network | 4.7 km | 950 attoseconds | 18 hours |
Generates ultralow-noise optical pulse train serving as the primary timing reference.
Measures timing differences between optical pulses with attosecond sensitivity.
Synchronizes optical and microwave sources by comparing pulse train with RF signals.
Adjusts timing in the fiber path based on error signals to maintain synchronization.
One of the most significant hurdles involved managing pulse propagation effects in the fiber links. Even with the most stable master laser, timing signals would degrade due to:
The feedback system successfully compensates for environmental fluctuations, but its effectiveness is limited by fundamental physical constraints:
Through meticulous engineering, they achieved a more than 10-fold improvement in timing stability compared with previous results1 .
"This will drive new scientific efforts towards the making of atomic and molecular movies at the attosecond timescale, thereby opening up many new research areas in biology, drug development, chemistry, fundamental physics and material science."
The demonstration of a complete laser-microwave network operating with attosecond precision across kilometer distances marks a watershed moment for ultrafast science. This technological breakthrough removes what had been a fundamental obstacle preventing attosecond-resolution photon science at hard-X-ray wavelengths1 .
As this timing distribution technology gets implemented at X-ray free-electron lasers and intense laser facilities worldwide, it will initiate nothing short of a revolution in how we study the atomic and molecular world. Scientists will transition from inferring ultrafast processes from static evidence to directly observing them unfold in "molecular movies" with both atomic spatial resolution and attosecond temporal resolution.
The implications extend beyond photon science facilities to fields including gravitational-wave astronomy, coherent optical antenna arrays, and ultra-stable optical clock comparisons, all of which require similarly extraordinary timing precision.
In the relentless pursuit of precision that has characterized scientific progress for centuries, the attosecond barrier represented one of the final frontiers. With this achievement, we haven't just refined existing technology—we've opened a door to observing nature at its most fundamental timescales, promising discoveries we haven't yet even imagined.