New Approach May Enable Portable Atomic Clocks

| December 10, 2014

A team of researchers from MIT and Draper Laboratory has developed a unused approach to atomic timekeeping that may make able more stable and accurate portable small clocks.

What time is it? The respond, no matter what your initial relation may be — a wristwatch, a smartphone, or every alarm clock — will always trace back to the inappreciable clock.

The international standard for time is immovable by atomic clocks — room-sized apparatuses that lodge time by measuring the natural vibration of atoms in a vacuum. The oftenness of atomic vibrations determines the detail of one second — information that is beamed up to GPS satellites, what one. stream the data to ground receivers every part of over the world, synchronizing cellular and cable networks, rule grids, and other distributed systems.

Now a clump at MIT and Draper Laboratory has get to up with a new approach to inappreciable timekeeping that may enable more immovable and accurate portable atomic clocks, potentially the greatness of a Rubik’s cube. The assign places to has outlined its approach in the magazine Physical Review A.

While chip-sized minute clocks (CSACs) are commercially available, the researchers affirm these low-power devices — about the bulk of a matchbox — drift over time, and are not so much accurate than fountain clocks, the plenteous larger atomic clocks that set the cosmos’s standard. However, while fountain clocks are the principally precise timekeepers, they can’t have existence made portable without losing stability.

“You could offer one in a pickup truck or a trailer and take in a carriage it around with you, but I’m guessing it won’t deal actual well with the bumps on the thoroughfare,” says co-author Krish Kotru, a graduate student in MIT’s Department of Aeronautics and Astronautics. “We have a path toward making a knit together, robust clock that’s better than CSACs by a couple of orders of bigness, and more stable over longer periods of time.”

Kotru says similar portable, stable atomic clocks could be useful in environments where GPS signals have power to get lost, such as underwater or indoors, similar to well as in militarily “hostile environments,” in which place signal jamming can block traditional navigation systems.

Co-authors of the bank-notes include Justin Brown, David Butts, Joseph Kinast, and Richard Stoner of Draper Laboratory.

A alter in time

The team came up through the new atomic timekeeping approach by making several “tweaks” to the streamer method.

The most accurate atomic clocks today employment cesium atoms as a reference. Like quite atoms, the cesium atom has a mark frequency, or resonance, at which it oscillates. Since the 1960s, one second has been defined as 9,192,631,770 oscillations of a cesium atom between two energy levels. To allotment this frequency, fountain clocks toss dull clouds of slow-moving cesium atoms a scarcely any feet high, much like a pulsed jet, and measure their oscillations as they go over up, and then down, through a microwave streak.

Instead of a microwave beam, the arrange chose to probe the atom’s oscillations using laser beams, which are easier to control spatially and beseech less space — a quality that support in shrinking atomic clock apparatuses. While more atomic clocks also employ laser beams, they repeatedly suffer from an effect called “AC Stark artifice,” in which exposure to an electric theatre of war, such as that produced by a laser, be able to shift an atom’s resonant frequency. This shift can throw off the niceness of atomic clocks.

“That’s certainly bad, because we’re trusting the infinitesimal reference,” Kotru says. “If that’s somehow perturbed, I don’t know on the supposition that my low-quality wristwatch is evil, or if the atoms are truly wrong.”

To avoid this problem, greatest in quantity standard fountain clocks use microwave beams instead of lasers. However, Kotru and his team looked on the side of ways to use laser beams space of time avoiding AC Stark shift.

Keeping time, in small

In laser-based atomic clocks, the laser girder is delivered at a fixed frequency and intensity. Kotru’s team in the room tried a more varied approach, called Raman adiabatic expeditious passage, applying laser pulses of changing vehemence and frequency — a technique that is also used in nuclear magnetic resonance spectroscopy to prove features in individual molecules.

“For our approach, we turn on the laser beating and modulate its intensity, gradually winding it on and then off, and we take the commonness of the laser and sweep it throughout a narrow range,” Kotru explains. “Just through . doing those two things, you set off a lot less sensitive to these methodical effects like the Stark shift.”

In thing done, the group found that the recently made known timekeeping system suppressed the AC Stark resort by a factor of 100, compared with a conventional laser-based system. Unlike spring clocks, which shoot atoms more than a meter upwards in disposition to measure a single second, the team’s means measures time in intervals of 10 milliseconds — an approach that is less accurate than spring clocks, but much more compact.

“That’s mulct, because we’re not trying to be active the world’s standard — we’re hard to make something that would spasm in, say, a Rubik’s raise to the third power, and be stable over a sunshineight or a week,” Kotru says.

The stability and accuracy of the system, he says, should have existence comparable to that of microwave-based inappreciable clocks on today’s GPS satellites, what one. are bulky and expensive.

Going a step more distant, the team tested the system’s replication to physical forces. “Let’s utter one day we got it molecular enough so you could put it in your backpack, or in your excipient,” Kotru says. “Having it be accomplished to operate while you’re persuading across the ground is important.”

Just crumbling of physically shaking the system, the assign places to “created a displacement between the atoms and the laser gleam.,” moving the laser beam from verge to side as it probed the vast assemblage of atoms. Even under such simulated concussion, the system was able to standard the atoms’ resonant frequency, with a heaven-kissing degree of sensitivity.

The team is at once working to reduce the size of other components of the regularity, including the vacuum chamber and electronics.

“Additional miniaturization could finally result in a handheld device with stability orders of magnitude better than concise atomic clocks available today,” Kotru says. “Such a fraud would satisfy requirements for more technologically serving to add force applications, like the synchronization of telecommunications networks.”

This exploration was sponsored by Draper Laboratory.

Publication: Krish Kotru, et al., “Robust Ramsey sequences with Raman adiabatic rapid passage,” Phys. Rev. A 90, 053611, 10 November 2014; doi:10.1103/PhysRevA.90.053611

Source: Jennifer Chu, MIT News

Image: Christine Daniloff/MIT
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