Description
$^{171}$Yb$^+$ ions feature two optical clock transitions: an electric quadrupole (E2) transition at 436 nm and an electric octupole (E3) transition at 467 nm. These two transitions have very different properties due to the different electronic structure of their excited states. In particular, they have a large differential sensitivity to the fine structure constant α, so that tight limits on possible variations can be obtained by comparing their frequencies at various positions in spacetime [1].
Of the two transitions, the E3 transition ($^2$S$_{1/2}$, F=0 – $^2$F$_{7/2}$, F=3) is particularly suitable for precision spectroscopy: Its excited state features a yearslong natural lifetime [2], so that coherent interrogation times are not limited by the spontaneous decay. Additionally, the excited state sensitivity to external electric and magnetic fields is almost equal to that of the ground state, resulting in a weak differential dependence for the transition. This permits high accuracy in the realization of the unperturbed E3 transition frequency [3].
The E2 transition ($^2$S$_{1/2}$, F=0 – $^2$D$_{5/2}$, F=2), on the other hand, features a larger sensitivity to external fields, which makes it a suitable ancillary transition: Residual perturbing fields are investigated on a magnified scale and can improve the knowledge of the unperturbed E3 transition frequency when relative sensitivities are known [4]. However, the E2 transition coherent interrogation is limited to about 40 ms by the relatively short lifetime of its excited state.
Additional ancillary transitions without this limitation are provided between the F=3 and F=4 hyperfine states of the long-lived $^2$F$_{7/2}$ state and their Zeeman manifolds (in a static external magnetic field). We drive these transitions using microwave radiation at about 3.6 GHz to investigate magnetic field and tensor frequency shifts. Microwave spectroscopy is not limited by ion heating and finite laser coherence, which makes it a useful tool to resolve small frequency shifts within a short measurement time. We obtain coherent interrogation times exceeding 5 s, allowing us to resolve mHz shifts within hours. Dynamical decoupling pulse sequences can be used to coherently average the energy of ±m$_\text{F} $ Zeeman pairs. This suppresses the linear Zeeman shift and associated energy fluctuations while retaining sensitivity to frequency shifts depending on m$_\text{F}^2 $, including possible shifts due to violations of local Lorentz invariance.
[1] R. Lange , N. Huntemann , J. M. Rahm , C. Sanner, H. Shao, B. Lipphardt , Chr. Tamm, S. Weyers , and E. Peik, “Improved Limits for Violations of Local Position Invariance from Atomic Clock Comparisons”, Phys. Rev. Lett. 126, 011102 (2021).
[2] R. Lange, A. A. Peshkov, N. Huntemann, Chr. Tamm, A. Surzhykov, and E. Peik, “Lifetime of the 2F7/2 Level in Yb+ for Spontaneous Emission of Electric Octupole Radiation”, Phys. Rev. Lett. 127, 213001 (2021).
[3] C. Sanner, N. Huntemann, R. Lange, Chr. Tamm, E. Peik, M. S. Safronova, and S. G. Porsev, “Optical clock comparison for Lorentz symmetry testing“, Nature 567, 204 (2019).
[4] R. Lange, N. Huntemann, C. Sanner, H. Shao, B. Lipphardt, Chr. Tamm, and E. Peik, “Coherent Suppression of Tensor Frequency Shifts through Magnetic Field Rotation”, Phys. Rev. Lett. 125, 143201 (2020).
| Presenter name | Melina Filzinger |
|---|---|
| How will you attend ICAP-27? | I am planning on in-person attendance |
