Minimizing time-dilation in ion traps — Towards an optical clock with Coulomb crystals

We present the status of our new experiment to lasercool linear chains of
¹⁷²
Yb
⁺
and
¹¹⁵
In
⁺
ions for an optical clock based on the
¹
S
₀
-
³
P
₀
transition in
¹¹⁵
In
⁺
. We successfully have trapped and laser-cooled Coulomb crystals of
¹⁷²
Yb
⁺
ions in our new scalable ion trap that are used to characterize the trap and to sympathetically cool
¹¹⁵
In
⁺
ions. We could demonstrate an area of more than 65 μm, where the fractional frequency shifts due to time dilation are below 10
^-18
for both ions.