"Quantum logic is quite a new and absolutely fascinating field of physics and might - ultimately - lead to the 
fabrication of a quantum computer. And it could also aid the search for the "theory of everything" - the missing link between traditional physics and quantum physics. One of the fundamental questions hereby is whether fundamental constants possibly vary. To prove this in the case of the fine-structure constant, for instance, we have to measure the spectral lines of atoms (i.e. their inner structure) more accurately than ever before. Quantum logic spectroscopy provides such a method. Physicists from the QUEST Institute at the Physikalisch-Technische Bundesanstalt (PTB) and from the Leibniz University of Hanover have come one decisive step closer to this goal: instead of complex laser arrangements, all they need is one single laser source to bring a single magnesium ion to a complete standstill. Then they use this ion to determine the properties of another ion. The new method has been published in the specialized journal Applied Physics B."