Tag Archives: Time
FAIL
The fastest clock in the world, my ass.
Oooooh. It displays six whole digits past the decimal. Down to the microsecond. (can you sense the sarcasm?) It’s a display. Just because it reads that many digits doesn’t mean the measurement actually has that precision.
I’ve wanted to get a display that went to the picosecond for the lab, but have it flash 12:00:00.000000000000 the whole time. Add it to the list of my unadopted suggestions.
“I see no progress in this industry. These clocks are no faster than the ones they made a hundred years ago.” — Henry Ford
Bringing Home the Gold
From Google Maps to Gold Medal
Kristin Armstrong, who won gold in the Women’s Individual Time Trial in Road Cycling, got a GPS track when she rode the Beijing Olympic course in December of 2007
After returning home to Boise, Idaho, I exported the GPS data to several different formats, one of which I was able to launch with Google Earth. I was then able to trace the entire course from the comfort of my home half a world away and find a similar route to train on back in Boise. This capability along with having the elevation profile proved invaluable in my preparation for my Gold Medal race.
GPS relies on precise time, provided by some colleagues of mine, and knowing where the satellites are relative to the earth, which is aided by some other colleagues of mine. Woohoo! We won gold!
Dropping the Minus Sign
Or, in this case, the “not”
Why aluminum should replace cesium as the standard of time
The technique involved is neat: for some atoms you can find wavelengths where the AC Stark shift is the same for the two levels in the clock transition, so the atom is unperturbed by the presence of the trapping light. So you trap them in an optical lattice, with confinement like a far off-resonance dipole force trap (FORT). This means you can continue to confine the atoms while it is in the superposition where it is oscillating between the two clock states.
The big advantage of this method is that you can trap millions of atoms easily in an optical lattice and that should make such a clock much more robust than a fountain, while achieving at least the same kind of accuracy.
Actually, that’s not the big advantage. Fountains trap millions of atoms (even billions, depending on your collection technique). The advantages are that you’d keep that many atoms (fountains lose signal from the original collection because the cloud spreads out, so the number you toss is an order of magnitude bigger than the number that return), you can interrogate the atoms for a longer period of time (an advantage shared by ion trap clocks/frequency standards) and avoiding cold-collision frequency shifts (atoms in close proximity tend to interact strongly, as they can interact for a relatively long time, and this changes the state of the atom, introducing an error in the signal)
However, “at least the same kind of accuracy” isn’t enough. I’ve noted before that international standards are a political issue. Cesium beam standards are commercially available. Furthermore, dozens of labs have or are building fountains, at some investment of time and money to gain the expertise in doing so (because atomic fountains are not, nor are they likely to become, a commercially available item). The countries doing this will likely be reluctant to switch to a standard that requires even more money and acquired expertise in a new technique for marginal gain in accuracy and precision. Especially in light of how many new options for secondary standards have emerged in just the last decade — an even better candidate may emerge as technology advances.