Quantum logic spectroscopy of highly charged ions

• Applicants: Professor Dr. Piet Oliver Schmidt; Professor Dr. Andrey Surzhykov
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 366146996

Precision spectroscopy of highly charged ions (HCI) provides insight into atomic systems in which electrons are highly correlated, strongly relativistic, and experience strong internal fields. Thus, highly charged ions are very well suited to probe our understanding of physics under these extreme conditions. They are the most sensitive known atomic species to probe for possible changes in fundamental constants and offer advantageous properties to probe coupling of hypothetical dark matter fields to normal matter. For these applications, high precision optical spectroscopy of HCI is required. Prior to this project, the spectroscopic resolution of optical transitions in HCI was limited by Doppler-broadening to several hundreds of megahertz. In the first funding period we have demonstrated hertz-level spectroscopy of the 2P1/2-2P3/2 fine-structure transition in 40Ar13+ using quantum logic with a co-trapped Be+ ion, improving the spectroscopic precision by eight orders of magnitude compared to the previous state-of-the-art. We have determined the excited state g-factor and compared it to the best ab initio atomic structure calculations, revealing relativistic and quantum electrodynamic effects in such a few-electron system. Before the end of the first funding period, we expect operation of an optical clock based on this transition, including a systematic uncertainty evaluation, and measurement of the 36, 40Ar13+ isotope shift.For the second funding period we propose to build upon this success by extending the techniques to achieve the first hertz-level spectroscopy of highly charged calcium ions, specifically Ca14+, and apply it to test for hypothetical 5th forces. Calcium has five stable isotopes without nuclear spin, which renders this element ideal for searching for nonlinearities in the so-called King plot of isotope shifts. These nonlinearities arise within the Standard Model of particle physics, but any deviation from these predicted values could hint at new physics, such as a potential 5th fundamental force that couples electrons to neutrons, or other non-gravitational coupling between dark matter and normal matter.

• DFG Programme: Research Grants