Ytterbium multi-ion crystals for tests of fundamental physics
Physicists have been trying to unify the four fundamental forces. However, a quantum consistent theory for the general theory of Relativity (GR) and quantum mechanics has not yet been found and verified with experimental observations. Tests of the Standard Model (SM) of particle physics and the basic assumptions of the GR, namely Einstein’s equivalence principle (EEP), have been a long pursuit.
In our laboratory, we are using ytterbium ions to test some of the basic assumptions of fundamental physics that might lead to discovery of new physics/ to search for new physics beyond SM. The Yb+ provides favorable properties to perform search tests. The 4f135d2 2F7/2 state in Yb+ has high angular momentum which is favorable for the test of local Lorentz invariance (LLI) [1], one of the pillars of EEP. By utilizing the different sensitivities of its Zeeman sublevels to a potential violation of Lorentz symmetry [2], we performed the most stringent test of LLI to date with a single 172Yb+ ion [3]. We plan to further improve the sensitivity via extending this test with multiple ions.
We are also looking for new physics by investigating the composition of dark matter and a possible existence of a dark matter boson that couples the neutrons and electrons in an atomic system via isotope shift measurements [4]. Ytterbium has many different electronic structured states, providing many narrow transitions for isotope shift measurements. Via King plot analysis [4], dominating shifts that are not well known, namely mass shift and field shift, are suppressed and become linear terms. We look for nonlinearity in the plot to search and set bound on coupling strength and the mass of the new boson.
The experimental technics obtained and advanced in the LLI test and the isotope shift measurement allows us to extend our research into a novel cascaded multi-ion clock with the 2S1/2 → 2F7/2 electric octupole (E3) transition. With this, we plan to reach desired statistical uncertainties much faster than a single ion clock. Using this clock, we plan to investigate temporal variation of the fine structure constant by comparison to the electric quadrupole (E2) transition of Yb+ or to the transitions of other clock species.
References
[1] V. A. Dzuba, et al., Nat. Phys.12, 465-468 (2016).
[2] R. Shaniv, et al., Phys. Rev. Lett.120, 103202 (2018).
[3] L. S. Dreissen, et al., Nat. Commun.13, 7314 (2022).
[4] J. C. Berengut, et al., Phys. Rev. Lett.120, 091801 (2018).