Gp. Barwood et al., Subkilohertz comparison of the single-ion optical-clock S-2(1/2)-D-2(5/2) transition in two Sr-88(+) traps, PHYS REV A, 59(5), 1999, pp. R3178-R3181
A simultaneous observation of the optical-clock S-2(1/2)-D-2(5/2) transitio
n at 674 nm, in two separately trapped single Sr-88(+) ions, is reported. T
wo nominally identical miniature rf Paul traps were used together with a 67
4-nm sideband-injection-locked extended-cavity diode laser. This "slave" la
ser was optically phase locked about 650 MHz away from a "master" diode las
er, which was itself lacked to a high-finesse, ultra-low-expansion (ULE) ca
vity. The ULE cavity was temperature-stabilized and suspended in an evacuat
ed enclosure, and provided an "optical flywheel" reference standard with a
relative drift rate of better than 1 part in 10(11) per hour. The differenc
e between center frequencies of the single Sr-88(+)-ion 673-nm (445-THz) tr
ansition multiplet in two traps was 120(90) Hz (one standard uncertainty).
Thus the two trap center frequencies agree to 3 parts in 10(13). [S1050-294
7(99)50405-8].