Researchers are designing a nuclear clock that would be two orders of magnitude more accurate than the most advanced atomic clock. It could someday be used in a new GPS, as the basis for secure communications, and to study fundamental theories of physics. The new clock will base its time keeping on the oscillations of a thorium ion’s nucleus. Atomic clocks use oscillating electrons to keep time, but these relatively light subatomic particles are affected by magnetic and electrical fields, causing them to drift by at least 4 sec/14 billion years (the estimated age of the universe). The new clock will use heavier neutrons, which should be less affected by these fields.
A laser in the clock operating at 1015 Hz will boost the nucleus of a thorium 229 ion to a higher energy state and make neutrons in the nucleus vibrate precisely. The ions need to be kept at temperatures in the 0.01°K range, a task usually handled by lasers for achieving ultralow temperatures. (Bombarding atoms with a properly tuned laser lowers the temperature by forcing atoms to absorb photons, along with their momentum, which slows or cools the atoms.) But bombarding the ions with a second laser to cool them would affect the accuracy of the clock. To get around this problem, researchers will include a thorium 223 ion with the 229 ion. The heavier, time-keeping ion will be unaffected by a cooling laser tuned to the lighter ion‘s frequency, but because of its proximity to the lighter ion, it will be cooled as well without degrading its vibrational frequency.
The major challenge facing the research team is determining the laser frequency needed to excite the thorium nucleus, and scientists have spent 30 years looking for that frequency.
The team includes scientists and engineers from the Georgia Institute of Technology, University of Nevada, and University of New South Wales, Australia.