Atomic Clocks Make a Quantum Leap in Accuracy

http://www.engineering.com/DesignerEdge/DesignerEdgeArticles/ArticleID/7029/Atomic-Clocks-Make-a-Quantum-Leap-in-Accuracy.aspx

by prateekj • 12 years ago

59 43 12 years ago

engineering.com

qianyilong• 12 years ago

The coolest part it that it improves both stability and accuracy. Cesium is often touted as a good clock but it only has good accuracy. The short-term stability has more noise than something like a Rubidium clock that is very stable on the short-term but inaccurate(relative to cesium anyway) on the long term.

This is cool because it is the best in both dimensions.

madengr2• 12 years ago

The phase noise (really short term stability) of a rubidium oscillator is rather poor compared to on ovenized quartz oscillator. So what I really want is a strontium disciplined OCXO.

mjb2• 12 years ago

Years ago I was involved in some work on clocks that needed very high performance at low cost. We ended up with OCXOs GPS-disciplined over some of their frequency and atomic clock disciplined (cesium, IIRC) over another part of the range.

Telling the time is hard.

prateekj4• 12 years ago

True! People use Rubidium clocks only because they are inexpensive. I don't think scientists working in expensive labs rely on Rubidium clocks.

adamlaiacano• 12 years ago

Some Rubidium clocks require very little power (700mW or less). This makes them ideal for under water applications where short term accuracy isn't an issue because the SONAR data transmission is going to be a mess anyway, and they provide much better long term stability than a crystal oscillator.

dchichkov• 12 years ago

Can I have a chip-scale one? With zero jitter? On every motherboard? Feeding TSC clock? Please? Pretty pretty pleaase?

prateekj4• 12 years ago

Definitely ... just as soon as it starts raining money ;)

guelo• 12 years ago

There are already very accurate clocks on your motherboard. Your problem has more to do with modern multi-processor design.

mjb2• 12 years ago

That depends on what you mean by accurate, and even then they pretty much suck. Clocks are "inaccurate" in a few ways. One of these ways is very short-term: variations in exactly when the clock edges arrive at frequencies near the clock frequency. Others of these are long-term: how far the clock is from it's target rate over decades. Between these there's a whole spectrum of different noise frequencies.

The oscillators on your motherboard, with very basic temperature correction, very basic calibration and only very basic quality control don't tend to do very well on any of these measures. They tend to do better on the high-frequency measures of clock badness, and worse on low-frequency measures, but they aren't stellar in any area. The end-to-end time system, including NTP and software-level drift correction, does an OK job in some circumstances. It does a horrible job in others.

If you go through life assuming your computer's local clock isn't literally out to get you, you're going to be disappointed.

thearn4• 12 years ago

Hate to be that guy when it comes to being pedantic about headlines, but wouldn't a `quantum leap` in accuracy be rather un-noteworthy?

derefr• 12 years ago

Or it could mean, in this case, a leap in what is considered to the smallest discernible difference (the quantum) of the measurement. ;)

prateekj4• 12 years ago

Quantum leap refers to a sudden increase in something. Given that this clock is 50% more precise than the previous record holder, I think it qualifies to be called a 'quantum leap'. So even if you are pedantic about headlines, it should still make sense. Don't you think so?

sczkid• 12 years ago

This might clarify what he meant: http://www.smbc-comics.com/?id=2628

musicaldope• 12 years ago

You'll never walk alone down the road of headline-aimed pedantry, friend

Oculus• 12 years ago

I can here to make that exact comment. It always irks me that a lot of people don't realize 'quantum' == 'small'.

bmm6o• 12 years ago

It depends heavily on the exact usage: http://dictionary.reference.com/browse/quantum?s=t

The salient feature here is that quanta are discrete and a transition from one to another is a jump rather than a smooth or continuous shift.

sabbatic13• 12 years ago

It's a Latin noun, derived from an adjective, that literally means "a something of some size." That's it. The first meaning in English is "some quantity." Uses which denote or connote 'large' or 'small' are secondary extensions which depend on context.

"Quantum leap" connotes an unpredictability in the magnitude of the change in common usage. Over time, the understanding has drifted a bit to include, usually, the idea of significant magnitude.

ghayes• 12 years ago

Not to be that guy, but Merriam-Webster is pretty clear on the definition: `a sudden large change, development, or improvement`[1]

http://www.merriam-webster.com/dictionary/quantum%20leap

dmd• 12 years ago

You (and everyone else who is commented in reply to you so far) didn't read the article.

In this particular case it is a perfect use of the phrase, as the advance in accuracy is based on measurements of the atomic electron transitions, also known as quantum leaps.

DanielBMarkham• 12 years ago

<random internet commentator tripe>This could be the basis of a future tricorder or Star Trek-like sensor array. Three ultra-sensitive clocks in an array should be able to infer mass and motion both for the unit and objects in the local area indirectly. Relativistic effects are minuscule, but not non-existent. Extremely-tuned clocks would have some pretty cool capabilities.</random internet commentator tripe>

splat• 12 years ago

One thing I've spent some time thinking about is whether it would be possible to use atomic clocks to get a better measurement of the gravitational constant G. (G is by far the most poorly known of all the fundamental physical constants.) The idea would be to build a sphere whose mass is very precisely known and place one clock near the mass and one clock far away. By measuring the gravitational time dilation you could infer G. As I recall from my order of magnitude calculations, atomic clocks would have to improve in accuracy by four orders of magnitude or so before this would be feasible. So it would still be a long ways off.

prateekj4• 12 years ago

Good point! The research group is still working on refining their system. So may be they will have another breakthrough in a year or two, you never know!

infogulch• 12 years ago

How about a wolframalpha link to those calculations? Assuming they're simple enough.

Also, would this require the clocks and mass to be far away from other large masses like the earth?

pilom• 12 years ago

In a vacuum, you could get GPS accuracy down to 700 nanometers with clocks that accurate [1]. If only that pesky atmosphere didn't get in the way!

[1] http://www.wolframalpha.com/input/?i=%281+second+%2F430+tril...

deletes• 12 years ago

There are also other problems than atmosphere.

http://eu.mio.com/en_gb/global-positioning-system_gps-accura...

danbruc• 12 years ago

Does it beat the pulsar clock [1]? And will standing next to clock make it go wrong because of the change of the gravitational field?

[1] http://en.wikipedia.org/wiki/Pulsar_clock

kabdib• 12 years ago

Pulsars are actually pretty noisy. Starquakes, infalling matter and braking due to drag on the magnetic field jink the rotational frequency around a lot, comparable to a good clock (you could probably compensate for the braking effects, but the quakes are another matter).

e3pi• 12 years ago

Ask: Such synchronous clocks possible?

Special and general relativity steam-roll over synched digit accuracy, at introducing any object's mass, any object's displacement.

Not gain or lose over five billion years?

How many digits this time?

Tides, quakes, rain on the roof, defeat the possibility of unbounded synched accuracy.

Daniel_Newby4• 12 years ago

Indeed. The best existing atomic clocks need to be recalibrated if they are raised a few centimeters, owing to gravitational time dilation.

gardarh• 12 years ago

One thing I'm really curious about: How can you measure the accuracy of the world's most accurate clock?

By definition there would be no more accurate timing device to benchmark it against so is the accuracy cited in the article only theoretical?

Daniel_Newby4• 12 years ago

Build several identical clocks and watch the ensemble drift relative to each other.

The lattice clock in this story has numerous clusters of atoms. They could fill only a few clusters and measure the performance relative to a good clock, then statistically derive how much it would improve by using the full set of clusters.

yetanotherphd• 12 years ago

They built two of them, and found that they agreed to within their nominal accuracy.

ChuckMcM2• 12 years ago

At this level of accuracy things are pretty strange. It used to bug me when you had to tune RF circuits at a distance with non-conductive tools because your body capacitance would throw the tuning off. Having a clock that just being near it will change what time it reads, well that is a whole different ballgame of weird is it not?

On a science note, why isn't this a gravity wave detector anyway?

Daniel_Newby4• 12 years ago

Gravity wave detectors get phase accuracy by comparing a photon to itself using an interferometer. SNR is improved by brightening the laser and averaging over more photons. The laser frequency is less important.

It turns out there are some ultraviolet nuclear transitions. The line widths promise to be obscenely narrow. If they can get it working in a clock, they will be able to directly measure gravitational time dilation of small masses.

ChuckMcM2• 12 years ago

Do you have a reference to the UV transitions? I'm sure the LIGO folks think of themselves as being in a race with advancing clock technology with regards to actually detecting gravity waves.

MichaelGG3• 12 years ago

Meanwhile on servers running Windows, keeping sync to within a few seconds is a mighty challenge, esp. with Hyper-V. (Linux guests have no issue with ms or sub-ms accuracy.)

Microsoft's Win32 time is only meant to prevent Kerberos error, so under 5 minutes is "fine".

grecy3• 12 years ago

If you're using win32 time for anything that needs accuracy greater than a few seconds, I think you're doing it wrong.

MichaelGG3• 12 years ago

Do you know of anything more accurate, especially under Hyper-V? I've tried installing ntpd and even using the most aggressive settings and host time sync off, they drift like mad and the system log is filled with kernel warnings about time changes.

Atomic Clocks Make a Quantum Leap in Accuracy

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