These clocks are so accurate they will lose just a second if they last the age of the universe. That's 14 billion years.
But they won't be used to keep the trains running on time. The clocks' exquisite precision, outlined in Nature today, the means they can measure, are space-time distorts under gravity forces.
Eventually, astrophysicists could enlist their help to detect mysterious dark matter.
More immediately, the clocks could tell us what's going on inside the earth by precisely mapping our planet's bumps and lumps – if the clocks are shrunk, that is.
Study co-author Will McGrew, a PhD student at the National Institute of Standards and Technology in the US, said clocks "ticking" is produced by emitted when electrons in ytterbium are excited by lasers.
It turns out they tick, it's almost perfect unison, 500 trillion times a second.
"Measuring time and frequency with incredible accuracy provides a really powerful lens to view the natural world," Mr McGrew said.
Atomic time 101
Measuring time was based on astronomy. For instance, the length of day was determined by one spin of the Earth on its axis.
But astronomical phenomena tend to slow down or speed up.
Our days are lengthening, an extra 1.7 milliseconds per century, thanks to our gravitational tango with the moon.
So while astronomical time might be for timetabling and such, science demands precision.
And this is where atomic time shines.
Rather than looking to the heavens, this form of time-keeping into the waves of radiation is shaken off by atoms when they're bathed in a laser light.
They sound super futuristic, but atomic clocks have been around for more than 60 years.
The first atomic clock that was accurate enough to be used to be built in 1955 at the UK's National Physical Laboratory.
It was accurate to a second in 300 years.
Some 12 years later, the cesium atomic clock became the international time standard, and over time, atomic clocks became far more accurate.
Modern atomic clocks which use strontium or ytterbium instead of cesium lose one second every 300 million years or so.
More than time-keepers
Atomic clocks' precision means tested Albert Einstein's general theory of relativity predicted that time runs faster or slower under the influence of different gravitational forces.
In other words, a clock is placed on a satellite orbit earth, which is higher "gravity potential", it will tick faster than a clock at sea level.
And there are already atomic clocks around the Earth on satellite that take advantage of this time dilation effect.
We don't have the global positioning system, or GPS, without them.
Another use of satellite-mounted atomic clocks is to accurately map Earth's size, shape, orientation in space and mass distribution, collectively called "geodesy".
Satellite geodesy usually involves timing how long it takes to make the trip between distant points, such as shining a laser up to a satellite and timing how long it takes to bounce back to a receiver on Earth.
GPS geodesy is accurate to around a centimeter, said Matt King, who uses satellite geodesy at the University of Tasmania and was not involved with the study.
But clocks with a higher "tick" rate – that is, higher frequency – wouldn't have to use light at all. They can use the relativistic effects of gravity.
This is what Mr. McGrew and his colleagues wanted to achieve with their atomic clock.
Instead of cesium, they used ytterbium. The radiation waves were emitted by ytterbium atoms, and orders from magnitude faster than those from Cesium atoms.
In their paper, the team showed that the clocks were exceptionally stable – losing almost imperceptibly – ticking almost perfectly in unison.
So by comparing the ticking difference between two clocks to separate continents, a person could feasible measure the difference between the clocks to under a centimeter.
Harnessing the precision of ultra-sensitive atomic clocks will be like having a "telescope looking within," Professor King said.
"Let's say you have an earthquake," he said.
"If you can measure that really, you can learn about the fundamentals of the interior of the earth, like its viscosity or runniness."
How the Earth bounces back when glaciers melt or sinks when groundwater's pumped out, too, can be tracked with atomic clocks.
The ground lifts and subsides, the event on a sub-centimeter scale, tell volcanologists how magma is a moving around below, Professor King added.
"Combine that with seismology, and you get a real picture of what's happening on the inside."
Big applications, compact clock
So what's stopping atomic clocks being wheeled out of volcanic and earthquake-risky places around the world?
Simply, the ytterbium clocks are big to move.
"[The clocks] "Take a fairly large laboratory," Mr. McGrew said.
This is because they need a bunch of large lasers to work.
A couple of lasers cool ytterbium at a fraction over absolute zero (-273 degrees Celsius), while others hold the chilled atoms in place.
Mr. McGrew and his colleagues have already started work on shrinking the systems.
Professor King is optimistic that ultra-precise atomic clocks will be used to be used on Earth as well in space.
"Computers are used to fill the whole rooms as well.
"We might be 20 years away, it might be soon, but if these [ytterbium clocks] can be miniaturized and if the precision keeps on increasing, then there's no shortage of applications. "
Weird and wonderful
Down the track, atomic clocks could be used for experiments that involved measuring the lowest distortions in space-time, like the extremely subtle stretching and squashing of matter caused by a gravitational wave.
Take dark matter, for instances. The astrophysicists know dark matter is out there, and that forms around the quarter of all the mass and energy in the universe.
But its "dark" nature – that it doesn't seem to reflect, absorb or radiation – means it is very difficult to detect.
One model of dark matter suggests it might interact with ordinary matter by changing the fundamental constants of nature, Mr. McGrew said.
And this is where atomic clocks might help astrophysic learners a little about the elusive stuff.
"Say there's a big dark matter that passes through a laboratory that has a clock and a strontium clock," Mr McGrew said.
"[The dark matter] would affect most factors, and then strontium by some other factor.
"By measuring the difference between the two clocks, you can detect the dark matter object's presence.
"These are extremely subtle effects, but when you can make measurements with digits of accuracy, you can detect them."
And, of course, we are not yet dreamed of.
"The first made atomic clocks who did not know they were building a GPS device," Mr. McGrew said.
"I think there's something similar to be said about atomic clocks – that is most important, most important applications haven't been thought of yet."