A laser beam usually quivers slightly, like a plucked string. In optical clocks, that quiver turns into timing errors. Engineers swapped the shaky light for steady light, and rubidium vapor clocks started ticking five times more evenly.

Inside the frequency standard, the laser light makes rubidium atoms absorb energy in strictly defined chunks. Seconds are counted by the number of such absorptions. If the beam quivers, atoms get confused, and the count drifts. The new laser, grown on a silicon chip, emits light with a linewidth below 10 hertz, like a note played without vibrato. Its quality is measured by a Q factor above 130 million.

With such light, rubidium atoms respond more sharply, and the clock gains accuracy faster. Over one second of measurement, the instability was 2×10⁻¹⁴: that's like measuring a kilometer with an error the width of a hair. Previous versions of such clocks had five times more scatter. The device stays compact and can work outside the lab, for example on a satellite or in field equipment.

Such a frequency standard is a step toward navigation without GPS, where precise time is kept onboard. And toward communication networks with synchronization better than today's.