报告摘要：
In 2012, we proposed multi-ion spectroscopy to improve the stability of optical ion clocks which is fundamentally limited by the quantum projection noise of the single ion. Multi-ion clocks will not only improve the stability by exploiting the higher signal to noise of multiple ions or their uncertainty by allowing for sympathetic cooling of clock ions using a separate ion species but will be the basis for future entangled clocks and cascaded clocks. For the multi-ion approach we have developed and qualified scalable high-precision ion traps, which are already in use in several experiments. A challenge is the high level of control of systematic shifts when scaling up a single trapped ion to a complex many-body system. I will discuss our results in characterizing the shifts in multiple trapped ions and from lessons learned the potential of multi-ion spectroscopy. The multi-ion clock is operated in a recent dedicated experiment, where 115In+ ions are sympathetically cooled by 172Yb+ ions. Here, I will report on the status of clock operation and international clock comparisons with fractional uncertainties at the level of low 10-18. Last but not least, I will briefly discuss new world-record limits we obtained in our work on an improved test of local Lorentz invariance using 172Yb+ ions and the search for new bosons using clock spectroscopy on even Yb+ isotopes.
报告人简介：
Prof. Dr. Tanja E. Mehlstäubler is a world-leading expert in precision optical spectroscopy. In her early career she studied francium and magnesium neutral atoms in a magneto-optical trap and investigated novel cooling methods for a Mg-based optical frequency standard. During her PostDoc at LNE-SYRTE in France, she brought her interests in quantum sensing to the cold atom gravimeter. Following another PostDoc with the Yb+ ion clock at PTB, she invented the idea of the "multi-ion" optical clock unifying the superb experimental control of single ions and the high signal-to-noise ratio of multiple quantum absorbers, as was previously only available in optical lattice clocks. In 2009, Tanja Mehlstäubler joined the QUEST Institute for Experimental Quantum Metrology at PTB, where she established her own research group. Since then, she develops high-precision scalable and integrated ion traps enabling 3D optical access for coherent laser manipulation and clock interrogation. With ion Coulomb crystals at hand, Tanja Mehlstäubler is fascinated by the complexity of the thermodynamics in such many-body systems. The physics of solitons and topological defects arising in 2D and 3D Coulomb crystal structures is just one of the pillars of her work group "Quantum Clocks and Complex Systems" at PTB. Furthermore, she is leading the multi-ion In+/Yb+ composite clocks experiment and is testing the limits of fundamental physics in engineered quantum systems.