Scientists from the National Institute of Standards and Technology (NIST) have managed to create a smaller version of the optical components that can cool atoms down close to absolute zero - a few thousandths of a degree from 0 Kelvins.

The miniaturized laser cooling setup, appearing in the latest edition of the New Journal of Physics,  is the first step in potentially integrating these systems on microchips - opening a wide range of applications in super-accurate atomic clocks, GPS-less navigation systems, precision measurement, and quantum system simulators.

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Cooling and Slowing Down Atoms

By cooling atoms, their temperature is decreased, which leads to slowing them down and allowing them to become more observable. At room temperature of about 20 degrees Celsius, atoms move in dry air at speeds close to the speed of sound, about 4.7 miles per second or 343 meters per second. At these speeds, its interactions with other atoms and the environment occur at extremely short periods of time, making events like atomic energy level transitions notoriously difficult to observe, much less measure.

However, cooling them to a crawl - moving down to 0.1 meters per second - allows researchers to measure these energy transitions, as well as quantum properties enough to be used as a reference for a variety of different applications.

For over twenty years, scientists have been using lasers to cool down atoms in an attempt to slow them down - this tech allowed NIST physicist Bill Phillips to share the 1997 Nobel Prize in Physics. With a careful choice of frequency and other properties, lasers can actually be used to cool down atoms instead of the light heating and energizing them up. Photons from these cooling lasers could reduce the momentum of atoms until they can be trapped in a special environment, like magnetic fields.

Conventional laboratory equipment required to achieve this effect is generally large - as large as a dining room table. This raises concerns on the portability and mobility of the tech, limiting its use outside the lab and in other specialized applications such as quantum simulators and navigation sensors.

Miniaturizing The Cooling Lasers

NIST researcher William McGehee, together with his team, has devised a "compact optical platform" about 5.9 inches (15 centimeters) long that can cool and trap gaseous atoms across a one-centimeter wide area. While other miniaturized versions of atomic cooling systems have been designed, this new NIST project relies on planar optics, which are significantly easier to scale commercially.

"This is important as it demonstrates a pathway for making real devices and not just small versions of laboratory experiments," McGehee said in a NIST news release.

The new miniaturized cooling laser relies on three optical elements: (1) light is projected from an optical IC through a device called an extreme mode converter, (2) this converter magnifies the laser beam originally 500 nanometers in diameter to a width 280 times wider, and (3) the magnified beam hits a fabricated ultrathin metasurface embedded with tiny pillars about 100 nm wide and standing at only 600 nm high.

These metasurface pillars proceed to magnify the laser to two more orders of magnitude, allowing it to capture and cool a larger area of atoms. The coverage of the metasurface is what miniaturizes the cooling process by allowing the beam to interact and cool atoms within its space.


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