[time-nuts] A better atomic clock design just published

[Brooks Shera]

Spin-1/2 Optical Lattice Clock

N. D. Lemke, A. D. Ludlow, Z. W. Barber, T. M. Fortier, S. A. Diddams, Y. 
Jiang, S. R. Jefferts, T. P. Heavner, T. E. Parker, and C. W. Oates

Phys. Rev. Lett. 103, 063001 (Published August 3, 2009)

A news article:

If your wristwatch was as accurate as today's atomic clocks, it would not 
gain or lose a second in 80 million years. In the United States, 
announcements of time come from Boulder, Colorado, which houses the atomic 
fountain clock that defines the second as 9,192,631,770 oscillations between 
the hyperfine ground states of the cesium atom.

Researchers are always looking for improvements to this current time (and 
frequency) standard, which is important for broadcasting and navigation. 
Single trapped ions and optical lattices offer two alternative systems that 
are being investigated. Nathan Lemke and colleagues at NIST in Boulder, 
Colorado, report an experiment in Physical Review Letters that uses atoms 
with a nuclear spin of 1/2 in an optical lattice for an atomic clock. An 
optical lattice clock benefits from being highly stable, and unlike other 
lattice clocks, Lemke et al.'s clock is based on spin-1/2 atoms, an atomic 
system offering experimental simplicity with the potential for high 
accuracy.

The NIST group traps and cools neutral 171Yb atoms and loads them into a 
one-dimensional lattice, so that about 30,000 atoms fill several hundred 
lattice sites. A laser drives an atomic transition between two energy levels 
in the Yb atoms, called the clock transition. The uncertainties in the 
measured transition frequency, arising from systematic effects-including the 
Stark effect, atomic collisions, inhomogeneous excitation of the atoms, 
ambient temperature, and laser noise-are measured to determine the clock's 
accuracy.

Lemke et al. compare their optical lattice clock with the current standard 
atomic fountain clock and find that the accuracy of the Yb lattice clock 
potentially challenges the current standard. - Sonja Grondalski