Characterization of a 88Sr+ optical frequency standard at 445 THz by two-trap comparison

Frequency stability and comparison measurements have been undertaken between a pair of optical frequency standards based on the
²
S
_½
-
²
D
_5/2
transition in independent trapped
⁸⁸
Sr
⁺
ions confined in two end-cap traps. A frequency stability of 2.5 × 10
^-16
at 4000 s has been measured, improving as τ
^-½
. A null frequency offset at the 3 × 10
^-16
level has been measured. A measurement of the ratio of the g-factors between the
²
S
_½
and
²
D
_5/2
levels has been made and indicates a small departure from LS coupling in the ion.