Direct Frequency-Comb-Driven Raman Spectroscopy of the 3D 2D3/2 − 3D2D5/2 Transition in Ca+ Ions: Isotope Shifts and the Search for New Physics Beyond the Standard Model

I will present high-resolution isotope shift spectroscopy of five calcium isotopes using direct frequency-comb-driven Raman transitions between the terahertz-spaced 3d
²
D
_3/2
and 3d
²
D
_5/2
levels. Fig.1.c) shows absolute frequency measurements on a single
⁴⁰
Ca
⁺
[1]. The achieved relative accuracy of 5.5 × 10
^-12
is nearly a factor of five better than the previous best Raman spectroscopy [2], and is currently limited by the inaccuracy of our atomic clock reference. By performing similar measurements on
^42,44,46,48
Ca
⁺
ions, we determined the isotope shift of this transition with an accuracy of about 25 Hz. These measurements in combination with precise measurements of the 4s
²
S
_1/2
- 3d
²
D
_5/2
transition are today's best isotope shift measurements to our knowledge and allow for improved bounds on new physics beyond the standard model [3].