A two-ion crystal composed of a highly charged heavy ion under study and a logic ion.

Research

A two-ion crystal composed of a highly charged heavy ion under study and a logic ion.
Image: Peter Micke

The goal of our research group is to study highly charged heavy ions, their forbidden optical quantum transitions, and the fundamental laws of nature.

High-precision laser spectroscopy has long been established for neutral and singly charged ions. The most precise of such spectroscopic measurements are done with optical atomic clocks. For highly charged ions, however, additional challenges arise, as so-called fast cycling transitions for laser cooling and state detection are not available. Sympathetic cooling and quantum logic spectroscopy nevertheless make it possible to realize such experiments. For this purpose, an extremely cold two-ion crystal is prepared in an ion trap. It is composed of the highly charged ion to be studied and a logic ion. The forbidden optical transition of the highly charged ion is then excited with a laser pulse (clock pulse). Next, the quantum state can be mapped onto the qubit of the logic ion using two successive quantum gates (SWAP gates). Finally, binary readout of the qubit can be carried out with high fidelity.

Algorithm for quantum logic spectroscopy. After the spectroscopy ion has been excited by a clock pulse, its quantum state is mapped onto the qubit of the logic ion via two successive swap gates. There, it can be read out with high detection fidelity.

Image: Peter Micke

This was successfully demonstrated a few years ago for a highly charged ion of intermediate charge state as part of a joint project of the Physikalisch-Technische Bundesanstalt and the Max Planck Institute for Nuclear Physics [Micke, P., Leopold, T., King, S.A. et al. Nature 578, 60–65 (2020)External link] and, shortly thereafter, the first optical clock based on a highly charged ion was implemented [King, S.A., Spieß, L.J., Micke, P. et al. Nature 611, 43–47 (2022)External link].

Heavy ions in their highest charge states feature further challenges, but also remarkable opportunities. A single electron bound to a heavy atomic nucleus, such as that of lead, is exposed to the strongest electromagnetic fields we have access to in a laboratory. Fundamental theories, such as quantum electrodynamics, can be tested under these extreme conditions with high sensitivity. Furthermore, these ions are highly promising for the search for unknown physics beyond the Standard Model of particle physics.
Our research group is setting up a new spectroscopy experiment at the GSI Helmholtz Center for Heavy Ion Research, where we have unique access to slow, highly charged heavy ions produced by an accelerator.

Our Research Topics

  • Ion trap development for optical spectroscopy
  • Application of a variety of ion production techniques including electron beam ion traps and accelerators
  • Laser cooling and sympathetic cooling techniques in ion traps
  • Full quantum control of individual trapped ions
  • Quantum logic spectroscopy
  • Optical clocks and frequency metrology, clock comparisons
  • Tests of fundamental physics and physics at the interface of atomic and nuclear physics
  • Searches for unknown physics beyond the Standard Model

Link to the Helmholtz Investigator GroupExternal link at the Helmholtz Institute Jena