A new kind of miniature atomic clock could provide weeks and months of better time than existing systems. Researchers at the National Institute of Standards and Technology (NIST) in collaboration with researchers at Georgia Tech have created a chip-on-chip clock that is the first of its kind. His work has been published Nature Communication.

Atomic clocks come in many forms, but one of the oldest and most iconic designs is made using atomic rays. These clocks send a beam of atoms through a vacuum chamber. At one end of the room, atoms enter a certain quantum state and begin to “click”. At the other extreme, click speed is measured or “read”. Using the full ticking rate of atoms, other clocks can be compared to atomic ray clocks and adjusted to match their times.

NIST has been using atomic rays to measure time since the 1950s. For decades, ray clocks have been used to maintain the primary standard for seconds and are still part of the NIST National Timing Society. Ray clocks are accurate, stable, and accurate, but they’re not very portable right now. The vacuum chambers in which atoms move are key to the success of these clocks, but they are impractical in part because of the size of the microwave cavity used to detect atomic “click”. The last ray clock used for the main US frequency standard, NIST-7’s vacuum chamber was over 2.5 meters or 8 feet long.

Smaller commercial clocks the size of a briefcase are common, but they still require a significant amount of power (about 50 watts) to run. For comparison, normal operation of smartphones requires about a third of the Watt.

Chip scale atomic clocks (CSAC) were developed by NIST in 2001. Advances in microfabrication allowed NIST to create steam chambers, tiny chambers the size of a grain of rice in which clock atoms are held and measured; The entire clock is the size of a piece of sushi. These watches consume very little power and can run on batteries to provide time in critical situations where GPS cannot reach.

CSACs have found numerous applications in underwater oil and gas exploration, military navigation, and even telecommunications. However, the timing of the clock tends to deteriorate as the temperature changes and the gas surrounding the atoms deteriorates.

“The CSAC is low-power and high-performance for its size. “It’s a great device, but it drags after a few thousand seconds of operation,” said William McGehee, a physicist at NIST. “The beam clock has been around since the 1950s and is stable, but still very requires a lot of energy. What if we could combine the best of these two systems?”

Using microfabrication techniques from CSAC, the group fabricated a chip-scale atomic beam device using a stack of etched layers of silicon and glass. This device is a very miniature version of the cameras used in atomic clocks like the NIST-7 and is about the size of a postage stamp.

Atomic vapor cell construction techniques developed at NIST and etched microcapillary arrays developed at Georgia Tech have played a key role in shrinking the vacuum chambers of larger beam clocks.

In the device, one chamber contains a small rubidium pill. This chamber is heated by releasing a stream of rubidium atoms through micro capillaries, which are channels only 100 micrometers wide. These tiny channels are connected to another chamber by materials that can absorb or collect individual gas molecules called non-evaporative acceptors, or NEGs, by dragging and collecting rubidium atoms, keeping the vacuum in micro capillaries clean. Tiny graphite rods also help collect dispersed atoms in the process.

This chip-scale beam device is now a prototype for a miniature atomic beam clock. Initial chip-scale tests of the beam clock showed performance to be slightly worse than current CSACs, but the team sees a way to improve stability. The researchers hope to further increase their accuracy by a factor of 10 and exceed the stability of existing CSACs by a factor of 100 on weekly timescales. Source