Ions in a Paul trap are highly isolated from their environment and yet readily controlled with high accuracy and precision. This rare combination has made Paul trapped ions a leading platform for research fields which rely on quality control and low noise: quantum information sciences and precision metrology. In this talk I’ll focus on an instance of the latter, but involving techniques from the former.
Isotope shifts (ISs), the isotope-dependent energy shifts of atomic energy levels, have long served as an important tool for studying nuclear and atomic structure. Recently, ISs have also been suggested as possible probes of beyond standard model (SM) physics: an additional fifth force that couples electrons to neutrons – such as would be mediated by some dark matter candidates - can alter electron energy levels in an isotope-dependent way. However, detection of these potentially minute effects demands an experimentally challenging precision of IS measurements.
Our solution to this challenge is a simple scheme which we realized as a proof-of-principle. We trapped two isotopes (88Sr+ and 86Sr+ in our case) together in a Paul trap. With a quantum information protocol, we entangled the two isotopes and prepared them in a state which is invariant with respect to dominant noise sources yet evolves due to the IS itself (but the entanglement is not necessary). Using this scheme, we measured a ~570 MHz IS with a relative uncertainty of 10^(-11). Moreover, we (almost unintentionally) measured the IS of the orbital magnetic moment for our chosen transition. Our scheme will hopefully pave the way for meaningful probes of beyond SM physics in tabletop experiments and present a significant advantage wherever precision IS measurements are useful.