Summary of Build the World’s Smallest Atomic Clock
In 1895, explorer Fridtjof Nansen lost his longitude due to unwound chronometers, forcing a conservative route. Modern GPS uses satellite atomic clocks for precision but remains vulnerable to interference. New research demonstrates a viable mobile atomic clock by shrinking the core vacuum chamber containing cesium vapor, enabling users to carry precise timekeeping directly in their receivers without relying solely on satellites.
Parts used in the Mobile Atomic Clock:
- Vacuum chamber
- Cesium vapor cloud
- Photons
- Electrons
- GPS receiver
For Fridtjof Nansen, 13 April 1895 started well. Six days earlier, the Norwegian explorer had set a new record for the closest approach to the North Pole, and now he was moving quickly over unbroken sea ice toward Cape Fligely and home. But then came a sickening realization: In his eagerness to break camp, he had forgotten to wind the chronometers. He had lost track of precise time, and thus the ability to track his longitude.
Although Nansen couldn’t have lost his position by more than a few minutes, it forced him to take a circuitously conservative route to avoid being swept into the North Atlantic. His expedition thus had to endure a hungry winter, camped on an unknown shore. Not until June the following year did he encounter other explorers and learn his true position—on Cape Felder, in Franz Josef Land.
Today, anyone with a smartphone can determine their time and position with ease. Satellites of the Global Positioning System (GPS) broadcast clock signals across the globe with uncertainties below 100 nanoseconds, or one ten-millionth of a second. These time signals carry the information needed for precise navigation: Because radio waves travel at exactly 0.299,792,458 meters per nanosecond (apart from minuscule variations due to refraction in the atmosphere), comparing signals from different satellites makes it possible to determine a position within a few meters. That’s why GPS has transformed seismic monitors, drone delivery, and many other applications.
But GPS can’t solve all timing problems. Central to the system are atomic clocks carried on each satellite. Although these clocks are extremely stable (and regularly calibrated by comparing them with ground-based atomic clocks at national standards laboratories), there are many ways to go wrong when transferring timing information to the user—jamming, spoofing, unintentional interference, solar storms, even reflections from buildings. But what if we could put this precision directly in the hands of the user by shrinking the atomic clock itself so it could work inside the GPS receiver? Would we, like Nansen, then want to carry our very best clocks with us?
In research now published at Physical Review Letters, we show that such a mobile clock is possible. We hope to make one soon.
The core of an atomic clock is a vacuum chamber containing a thin cloud of vaporized metal, usually cesium. Atoms in the vapor resonate at a precise frequency, meaning that their electrons will accept energy only from photons having just the right amount of it. If those photons have a little too much or too little energy—that is, if their frequency is a little too high or too low—the absorption falls off markedly. This is the key feature of an atomic clock.
Read more: Build the World’s Smallest Atomic Clock
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Why did Fridtjof Nansen lose track of his position?
Nansen forgot to wind his chronometers before breaking camp, causing him to lose precise time and the ability to track his longitude. -
How does modern GPS determine position?
GPS determines position by comparing signals from different satellites that broadcast clock signals with uncertainties below 100 nanoseconds. -
What are the limitations of current GPS systems?
Current GPS systems face issues such as jamming, spoofing, unintentional interference, solar storms, and signal reflections from buildings. -
What is the core component of an atomic clock?
The core of an atomic clock is a vacuum chamber containing a thin cloud of vaporized metal, usually cesium. -
How do atoms function within an atomic clock?
Atoms in the vapor resonate at a precise frequency, accepting energy only from photons having the exact right amount of energy. -
What happens if photon frequency is incorrect in an atomic clock?
If the photon frequency is too high or too low, the absorption of energy falls off markedly. -
Can atomic clocks be made small enough for personal use?
Research shows it is possible to shrink the atomic clock so it can work inside a GPS receiver for user access.
