An optical lattice atomic clock built by a collaboration of researchers from the National Institute of Standards and Technology in Boulder, Colo., and from the Siberian branch of the Russian Academy of Science’s Institute of Laser Physics in Novosibirsk demonstrates that it should be possible to use even-numbered isotopes of neutral atoms in the instruments, improving their accuracy and short-term stability. The work was reported in the March 3 issue of Physical Review Letters.

Such clocks, in which the cold clouds of atoms that serve as the oscillator are trapped in a 1-D optical lattice, may improve the performance of time standards, offering benefits in communications and navigation and enabling investigators to probe whether fundamental physical constants such as the fine structure constant vary with time. Hitherto, they have required the use of odd-numbered isotopes, which are highly sensitive to magnetic fields and to the polarization of the lattice light, compromising their performance. Even-numbered isotopes do not display these problems, but they had resisted the direct optical excitation of a desired clock transition.

The scientists discovered that the application of a stable, 1.2-mT magnetic field to the setup enables them to access this transition in ¹⁷⁴Yb using 578.42 nm light from a dye laser. They note that the approach should be compatible with even-numbered isotopes of neutral strontium, calcium and magnesium atoms, and that it could simplify the use of 2- and 3-D optical lattices in the clocks.