
Atomic Clocks Make a Quantum Leap in Accuracy - prateekj
http://www.engineering.com/DesignerEdge/DesignerEdgeArticles/ArticleID/7029/Atomic-Clocks-Make-a-Quantum-Leap-in-Accuracy.aspx
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pilom
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...](http://www.wolframalpha.com/input/?i=%281+second+%2F430+trillion%29+*+speed+of+light)

~~~
deletes
There are also other problems than atmosphere.

[http://eu.mio.com/en_gb/global-positioning-system_gps-
accura...](http://eu.mio.com/en_gb/global-positioning-system_gps-accuracy-
error-sources.htm)

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thearn4
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?

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

~~~
bmm6o
It depends heavily on the exact usage:
[http://dictionary.reference.com/browse/quantum?s=t](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.

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ChuckMcM
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_Newby
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.

~~~
ChuckMcM
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.

~~~
Daniel_Newby
[http://arxiv.org/abs/1110.0741](http://arxiv.org/abs/1110.0741)

[http://www.thorium.at/?page_id=4](http://www.thorium.at/?page_id=4)

I could not find many references, but I think clocks mainly make the
instrument cheaper, or possible in the case of long-baseline satellite
instruments.

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qianyilong
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.

~~~
madengr
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.

~~~
mjb
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.

~~~
madengr
Cool. I bought a couple of HP Z3801A recently for home lab use. Also have an
Arbiter GPS disciplined clock at work as a frequency standard for my RF
equipment; they use one of the Wenzel OCXOs that has the lowest phase noise
you can buy.

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gardarh
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?

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

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DanielBMarkham
<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
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.

~~~
infogulch
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?

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e3pi
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_Newby
Indeed. The best existing atomic clocks need to be recalibrated if they are
raised a few centimeters, owing to gravitational time dilation.

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

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

~~~
mjb
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.

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danbruc
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](http://en.wikipedia.org/wiki/Pulsar_clock)

~~~
kabdib
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).

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MichaelGG
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".

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

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MichaelGG
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.

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grecy
If I have something that needs that level of accuracy, and the implied up time
to go with it, I don't use Windows. Neither should you.

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MichaelGG
I guess I find it sort of amazing that Windows can ship in 2014 and not have
close to ms accuracy.

~~~
grecy
Not at all. I think that kind of thing highlights where Microsoft's priorities
are with Windows, and therefore the kinds of things you should be doing with
it.

If you buy a civic to take to the racetrack, you shouldn't be amazed it
doesn't come with a roll cage. Civics are supposed to be on racetracks, and
windows isn't supposed to be a serious-workload OS. It's no problem though,
you have plenty of alternatives for both.

