NIST Ytterbium Atomic Clocks Set Record For Stability

New submitter bryanandaimee writes "An optical lattice clock like the one discussed earlier on Slashdot has broken the stability record. Comparing two OLC's using trapped atoms of Ytterbium, the stability of the clocks was measured to 2 parts per quintillion (10^18). While the previously reported OLC used strontium, these clocks, built by another group, use Ytterbium. Interestingly, while the stability of the clocks is now the best in the world, the accuracy has yet to be measured."

Comments

Re:Weird choice of measurements

[AdamHaun]

Accuracy measures how close the frequency is to the target, on average. Stability measures how the frequency drifts over time (and temperature, etc.). Accuracy is more of an absolute measurement while stability is more of a relative measurement. From the article:

The ticks of any atomic clock must be averaged for some period to provide the best results. One key benefit of the very high stability of the ytterbium clocks is that precise results can be achieved very quickly. For example, the current U.S. civilian time standard, the NIST-F1 cesium fountain clock, must be averaged for about 400,000 seconds (about five days) to achieve its best performance. The new ytterbium clocks achieve that same result in about one second of averaging time.

and

[U.S. civilian standard cesium reference clock] NIST-F1's performance is described in terms of accuracy, which refers to how closely the clock realizes the cesium atom's known frequency, or natural vibration rate. Accuracy is crucial for time measurements that must be traced to a primary standard. NIST scientists plan to measure the accuracy of the ytterbium clocks in the near future, and the accuracy of other high performance optical atomic clocks is under study at NIST and JILA.

So it sounds like accuracy is defined in terms of how well the clock reproduces the ideal frequency of the physical process it's based on. Hopefully there's a physicist or two around who can give us the exciting details.

Re:Weird choice of measurements

[maxwell demon]

Imagine a mechanical clock that has such a heavy minute hand that it goes much faster down than up. But it returns after exactly one hour, and even after ten years, it shows the full hour accurate to the second. This is a clock with very low stability, but quite high accuracy (for a mechanical clock, for an atomic clock that would of course still be terrible accuracy).

On the other hand, imagine a mechanic clock which doesn't have this stability problem, but the pendulum is not compensated for temperature changes. That is, when it gets warmer, the pendulum gets slightly longer and the clock goes slightly slower. Now temperature doesn't change very fast, so you'll not notice the effect in a short time span. However over time, the clock will drift away from the correct time, unless you manually correct it. This is clock with good stability, but not so good accuracy.