As arguably one of the best and most well-known theories in contemporary physics, quantum electrodynamics (QED) has been the subject of many rigorous tests. The SPECTRAP experiment aims to be one of them by checking the QED predicted effects known as "vacuum polarization" and "self energy". These contributions to the energy of an electron become very significant in high electric fields, such as exist around the cores of high-Z atoms. Therefore, one aims to produce heavy ions fully stripped of electrons down to a single one in the ground (hydrogen-like) state and do laser spectroscopy on it.

Similar experiments with e.g. Pb⁸¹⁺ or Bi⁸²⁺ have already been performed at various places, however the accuracy was limited because of high ion velocities. For this reason, in order to minimize the Doppler effect (i.e. increase the accuracy), the ions in this experiment are going to be trapped in a Penning trap and cooled down to cryogenic (liquid helium) temperature. At the same time, the trap's axial and radial optical transparency will allow for laser irradiation and detection of fluorescent photons coming from the excited ions. 

1. "Laser cooling of externally produced Mg ions in a Penning trap for sympathetic cooling of highly charged ions" Z. Andjelkovic, R. Cazan, W. Nörtershäuser, S. Bharadia, D.M. Segal, R.C. Thompson and M. Vogel , Phys. Rev. A 87 (2013) 033423
2. "Non-destructive single-pass electronic detection of ions in a beamline", Stefan Schmidt, Tobias Murböck, Zoran Andelkovic, Manuel Vogel, Stefan Stahl, Gerhard Birkl, Wilfried Nörtershäuser, Rev. Sci. Inst. 86 (2015) 113302
3. "A compact source for bunches of singly charged atomic ions", T. Murböck, G. Birkl, S. Schmidt, W. Nörtershäuser, Z. Andelkovic, and M. Vogel, Rev. Sci. Inst. 87, 043302 (2016)
4. "Rapid crystallization of externally produced ions in a Penning trap", T. Murböck, S. Schmidt, G. Birkl, W. Nörtershäuser, R.C. Thompson and M. Vogel, Phys. Rev. A 94 (2016) 043410
5. "Sympathetic cooling in two-species ion crystals in a Penning trap", S. Schmidt, T. Murböck, Z. Andelkovic, G. Birkl, K. König, W. Nörtershäuser, R.C. Thompson and M. Vogel, J. Mod. Opt. 65 (2017) 538, 1