Why are atomic clocks so accurate?

In summary, the accuracy of a clock is defined by its Q factor and inherent noise. Atomic clocks are highly accurate due to the stability of the hyperfine transition of the cesium atom, which has a Q factor of > 1011. This is because the energy levels involved in the oscillations are very long-lived, making them very "sharp" in frequency. However, the stability of an atomic clock also depends on technical factors such as sensitivity to external factors and the ease of manipulating the atoms. The most accurate atomic clocks use a combination of hydrogen masers and cesium fountains to achieve short-term and long-term accuracy, respectively. Other options for short-term stability include cryogenic dielectric resonators, which can have an ADEV
  • #1
iVenky
212
12
For any clock, the way I define accuracy of the clock is based on the Q factor (the ability to reject noise) and the inherent noise in the system. In that case, can you explain me why atomic clocks are so accurate? Do they have high Q factor? (if so, how)? or low noise to begin with?
 
Physics news on Phys.org
  • #2
iVenky said:
For any clock, the way I define accuracy of the clock is based on the Q factor (the ability to reject noise) and the inherent noise in the system. In that case, can you explain me why atomic clocks are so accurate? Do they have high Q factor? (if so, how)? or low noise to begin with?
Have you googled how an atomic clock works ?
It is likely to answer your questions :smile:

have a go and then come back with anything you don't understand
provide a link to the site so that we can see what you were readingDave
 
  • Like
Likes FactChecker, Cryo, phinds and 1 other person
  • #3
Hi,

I checked everywhere online and they all talk about how accurate the hyperfine transition of cesium atom is. Is it because there is not much loss mechanism involved here in this natural oscillation process for atoms?
 
  • #4
High Q is certainly important for accuracy, but, in general, I'm not sure it's the only factor. Think about a trombone (a slightly less accurate oscillator) but still high Q. If you move the slide the note changes, but the Q doesn't necessary change much. Or, consider a quartz crystal oscillator. The most stable ones have a temperature controlled oven for the crystal to stabilize the frequency, even though the Q isn't effected much.
 
  • #5
iVenky said:
Hi,

I checked everywhere online and they all talk about how accurate the hyperfine transition of cesium atom is. Is it because there is not much loss mechanism involved here in this natural oscillation process for atoms?

Because the oscillations per second is very well known and it is very stable over very long time periods,
as good as 1 second in 100 million years. That stability makes for a very accurate clock

I use a rubidium standard clock oscillator ( similar to a caesium one) in several of my microwave radio transceivers on
10 GHz and 24 GHz.
The unit produces a very stable 10MHz output that I use as a reference oscillator for the transceiver local oscillatorDave
 
  • #6
davenn said:
Because the oscillations per second is very well known and it is very stable over very long time periods,
as good as 1 second in 100 million years. That stability makes for a very accurate clock
like I said, my question is every more fundamental, why is it stable over very long time periods? I read atomic clocks have Q factor of > 1011 or something. Is the decay process (energy lost) involved in these oscillations super small? then I can understand why atomic clocks have high Q factor since Q=2*pi*energy stored/energy dissipated per cycle
 
  • #7
iVenky said:
why is it stable over very long time periods?

that is just the nature of the ceasium atom

"why" questions can't really be answered as they always just lead to another "why" question
 
  • #8
iVenky said:
like I said, my question is every more fundamental, why is it stable over very long time periods
Try attacking this question from the other direction: what things cause instability in other clocks? Are these factors present in a cesium clock?
 
  • Like
Likes davenn
  • #9
Nugatory said:
Try attacking this question from the other direction: what things cause instability in other clocks? Are these factors present in a cesium clock?
thanks ... good angle of attack :smile:
 
  • #10
iVenky said:
. Is the decay process (energy lost) involved in these oscillations super small? then I can understand why atomic clocks have high Q factor since Q=2*pi*energy stored/energy dissipated per cycle

Sort of. The energy levels involved are very long-lived making them very "sharp" in frequency.
However, this is only part of the story. The fact that the transition is stable in the long term also has to do with a variety of technical factors. When you add up the budget for a clock there are many, many issues. Some of them have to do with sensitivity to external factors (collisions with other atoms, sensitivity to external magnetic or electric fields, Doppler shifts etc) and some of them have to with how easy (relatively speaking) to manipulate the atoms. The latter will depend on which transitions are available, how easy it is to cool etc.

Note that there is no such thing as a "best" clock. What we call an "atomic clocks" are really a combination of two clocks: hydrogen masers have good short term accuracy and are used to generate the actual times signal (say 10 MHz). However, masers drift over longer times (say seconds) and are therefore "disciplined" using a cesium fountain (which by its very nature does not give a continuous time-signal out). Hence, the long-term accuracy is completely given by the accuracy of the Cs clock.
 
  • #11
f95toli said:
Note that there is no such thing as a "best" clock.
Perhaps not "best" but the most accurate clocks do have something in common and that is the very low level of interaction between the individual atoms and the bulk of the substance. That implies the active atoms need to be in a gas.
 
  • #12
sophiecentaur said:
Perhaps not "best" but the most accurate clocks do have something in common and that is the very low level of interaction between the individual atoms and the bulk of the substance. That implies the active atoms need to be in a gas.
sort of.
However, note that for short-term stability there are other options. Cryogenic dielectric resonators can have a short-term (up to tens of seconds) accuracy similar to or better than hydrogen masers. I believe an ADEV better than 1e-15 at about 10s has been reported for sapphire resonators which is something like an order of magnitude better than a hydrogen maser.
 
  • Like
Likes sophiecentaur
  • #13
f95toli said:
sapphire resonators
That's interesting. How does the interactions in such a condensed material not affect the resonance bandwidth? Why is there no line broadening?
 

1. Why are atomic clocks considered the most accurate timekeeping devices?

Atomic clocks are considered the most accurate timekeeping devices because they use the natural oscillations of atoms as a reference for measuring time. These oscillations are extremely consistent and precise, making atomic clocks more accurate than any other timekeeping method.

2. How do atomic clocks work?

Atomic clocks use the oscillations of atoms, specifically the element cesium, to keep time. The cesium atoms are excited to a specific energy level and then allowed to fall back to their ground state. This process creates a very precise frequency that is used to measure time.

3. How accurate are atomic clocks?

Atomic clocks are incredibly accurate, with an accuracy of one second in 100 million years. This means that they will only gain or lose one second over the course of 100 million years, making them the most accurate timekeeping devices in existence.

4. What is the importance of atomic clocks?

Atomic clocks are crucial for a variety of modern technologies and industries. They are used for precise timekeeping in telecommunications, GPS systems, financial transactions, and scientific research. They also help to keep our global time standard, Coordinated Universal Time (UTC), accurate.

5. How do atomic clocks compare to other types of clocks?

Compared to other types of clocks, such as mechanical or quartz clocks, atomic clocks are significantly more accurate. Mechanical clocks typically have an accuracy of one second per day, while quartz clocks have an accuracy of one second per week. Atomic clocks, on the other hand, have an accuracy of one second per 100 million years.

Similar threads

  • Atomic and Condensed Matter
Replies
4
Views
1K
  • Special and General Relativity
Replies
23
Views
950
  • Special and General Relativity
Replies
16
Views
576
  • Special and General Relativity
3
Replies
95
Views
4K
  • Atomic and Condensed Matter
Replies
3
Views
3K
  • Special and General Relativity
2
Replies
58
Views
3K
  • Other Physics Topics
Replies
27
Views
1K
Replies
38
Views
2K
  • Atomic and Condensed Matter
Replies
10
Views
1K
  • Atomic and Condensed Matter
Replies
4
Views
1K
Back
Top