A completely new kind of atomic clock could change the way we calculate time.
Unlike an atomic clock, which uses independent atoms to measure one second, the new quantum gas squeezes atoms together to measure time more accurately than ever before.
Since 1967, one second has been defined as the time it takes for one caesium electron to oscillate exactly 9,192,631,770 times.
Standard atomic clocks use thousands of ticking caesium atoms, which behave and are measured largely independently.
The new clock packs atoms much closer together. In the new device, strontium atoms are huddled into a tiny three-dimensional cube at 1,000 times the density of previous one-dimensional clocks.
This is what is called a quantum gas, and the atoms in such a gas are much more in sync than otherwise, meaning the clock’s ticks stay pure and stable for an unusually long time.This is the key to achieving increasingly accurate time-measurement.
This is the key to achieving increasingly accurate time-measurement.
“The most important potential of the 3D quantum gas clock is the ability to scale up the atom numbers, which will lead to a huge gain in stability,” says Jun Ye of the National Institute of Standards and Technology (NIST) and co-author of the paper published in the journal Science.
“The ability to scale up both the atom number and coherence time will make this new-generation clock qualitatively different from the previous generation.”
The experimental data shows the new quantum gas clock achieved a precision of just 3.5 parts error in ten quintillion (the number one with 19 zeros after it) in about two hours.
This makes it the first atomic clock to ever reach that threshold, and 20 times more accurate than its predecessor.
“This represents a significant improvement over any previous demonstrations,” Ye says.
While this is all fascinating from a scientific perspective, you might be wondering what the point is.
Why are we striving to reach incrementally better measurements of ‘one second’? Well, it turns out many threads of scientific research depend on the ability to know precisely how much time has passed.
Time dilation is one of the effects described by Einstein in his theory of general relativity.Essentially, gravity affects how quickly someone experiences time passing. On Earth, we may not feel this because it is so small, but it is still there.
Essentially, gravity affects how quickly someone experiences time passing. On Earth, we may not feel this because it is so small, but it is still there.
Today’s clocks are so precise that you can actually use them to measure the tiny gravitational effects we experience here on Earth, Poli says.
“Now, with the time accuracy we have today, for example, you can measure the difference of ticking rate between two clocks on Earth that are only separated one centimetre in height.”
This opens up a whole new set of possibilities of how to study the Earth itself.
“There are groups trying to perform a new kind of geodesy, based on comparisons of optical frequency standards located at different places on Earth.” Geodesy is the principle of using maths to work out the shape of our own planet.
Poli thinks more accurate clocks could be used to solve one of the biggest mysteries in the Universe so far; why general relativity and quantum mechanics don’t mix.
“My view for the future is to implement future accurate clocks to explore gravity itself, in previously unexplored regimes,” Poli says.
“I’m referring to the realisation of future quantum devices based on ultra-precise clocks to study the interplay between Quantum Mechanics and General Relativity. This is one of the least explored fields in physics today and any result along this line would be a groundbreaking result.”
For those of us who don’t spend our days contemplating why quantum effects are incompatible with theories of gravity, more accurate clocks have more practical, albeit prosaic benefits.
Everything from GPS to mobile phone calls and electronic transactions need a precise time reference. Any development in technology in the past has led to a new application.
A further breakthrough would likely improve such services, or create new ones.
But what is the ultimate limit?
“Theoreticians tell us that something will certainly happen at the Planck scale, which is extremely small,” says Poli.
The Planck time scale corresponds to the amount of time it would take light to travel the Planck length, which is 0.00000000000000000001 times the length of a proton.
In essence, it’s an uncomprehensively short amount of time, and we are nowhere near that level of accuracy yet. “It is at least 25 orders of magnitude away from where we are now,” Poli says.
On our way to achieving unprecedented accuracy, maybe we’ll stumble across something new.
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