Physics · the experiment
Probe strontium for twelve seconds
A silicon cavity cooled to a few kelvin, a laser steady to 7 × 10⁻¹⁸. Cool it down, then use it to probe strontium atoms for more than ten seconds at a stretch.
1 · Cool the cavity
Beginner
The laser's noise drops when the cavity goes from 16 K to 6 K. What does that drop show?
2 · Lengthen the pulse
Intermediate
A stability of 7 × 10⁻¹⁸ on a frequency of 194 THz means fluctuations of how much?
The laser drives a strontium clock. The longer the pulse that probes the atoms, the narrower the measured line. Lengthen it until you get the article's 64 mHz line.
3 · Find the limit
The excited state of strontium-87 used by the clock lives about 170 seconds.
Expert
With a perfect laser, what would happen with a pulse several hundred seconds long?
4 · Measure one day's drift
Tracked by the strontium clock, the cavity's frequency drifts slowly, by less than 4 µHz per second.
Expert
By how much does it drift at most in one day?
Strontium probed
—