Knowing what time it is down to the very last sliver of a second is easy — but only if you happen to have an atomic clock in your pocket. Unfortunately, most such devices wouldn't fit. In fact, there probably wouldn't even be room in the average studio apartment. But all that may be about to change.
Researchers at the Massachusetts Institute of Technology (MIT) are developing what they say is a highly accurate atomic clock the size of a Rubik's cube, measuring about 2 inches (5 centimeters) in each dimension. The clock could one day be used to keep time in places where conventional clocks, like the ones on a cell phone, don't work — like underwater or in war zones, where signal jamming limits connectivity to satellite networks — the researchers said.
Like other atomic clocks, the MIT prototype keeps time by measuring the natural vibration, or oscillation, of cesium atoms in a vacuum. All atoms oscillate at a particular frequency when they move between two energy levels, but since the 1960s, cesium's frequency has been used to define the length of one second. Essentially, one second equals 9,192,631,770 oscillations of a cesium atom. [Wacky Physics: The Coolest Little Particles in Nature]
To keep track of cesium's oscillations, scientists typically use what's known as a fountain clock: a huge tabletop covered in wires and high-tech equipment that looks nothing at all like the clock on your kitchen wall. Resembling a fountain spewing water at the sky, the clock tosses small clouds of cesium atoms several feet (more than 1 meter) into the air and then keeps track of how many times they oscillate, or move up and down, through a microwave beam.
It takes a big clock to keep track of more than 9 billion oscillations. So, to shrink one of these oversized instruments, the researchers decided to measure fewer oscillations at a time — 10-milliseconds' worth, to be exact. By multiplying the number of oscillations that occur in 10 milliseconds by 100, the researchers can estimate how many oscillations would occur in a full second. They also changed the beam that the atoms are moving through from a microwave beam to a laser beam, which is easier to control in a small space.
With these modifications, the MIT team was able to make its fountain clock much more compact than, say, the NIST-F2 — the cesium fountain atomic clock that serves as America's master clock at the National Institute of Standards and Technology in Boulder, Colorado. However, MIT's miniaturized atomic clock isn't nearly as accurate as the NIST-F2, which can keep time without losing or gaining a single second for 300 million years.
"That's fine, because we're not trying to make the world's standard — we're trying to make something that would fit in, say, a Rubik's cube, and be stable over a day or a week," Krish Kotru, a graduate student in MIT's Department of Aeronautics and Astronautics and co-author of a new paper outlining the clock project, said in a statement.
If the researchers can shrink their clock down to a portable size, it can be used in places where cell phones, which also run on atomic time, won't work. Submarine crews or deep-sea divers may even be able to use these highly accurate clocks underwater. Furthermore, soldiers on the battlefield could use the devices even if satellite signals are jammed, the researchers said.
There are other miniaturized versions of these clocks, known as chip-size atomic clocks (CSACs), already on the market. CSACs, which are about the size of a matchbox, solve the portability problem, but they sacrifice a lot of the preciseness of conventional atomic clocks, according to the researchers.
"We have a path toward making a compact, robust clock that's better than CSACs by a couple of orders of magnitude, and more stable over longer periods of time," Kotru said. "Additional miniaturization could ultimately result in a handheld device with stability [that is] orders of magnitude better than compact atomic clocks available today."
To test the alleged robustness of their new clock, the team simulated carrying the device over rugged terrain by moving the clock's laser beam from side to side as it probed the cloud of cesium atoms. But even with its laser beam shaking around, the clock still kept time accurately, according to the researchers.
“Let’s say one day we got it small enough so you could put it in your backpack, or in your vehicle,” said Kotru. “Having it be able to operate while you’re moving across the ground is important.”
Such a device, he added, could take on more high-tech applications, such as synchronizing telecommunications networks.