The grant entails 700.000 euros of funding for experimental research to help answer the intriguing question why simple proton-bearing molecules behave perfectly according to the laws of quantum physics, whereas deuteron-bearing species display unexpected anomalous behaviour.
Recently, the vibrational frequencies of the deuterated molecular hydrogen ion (HD+) were measured with record-breaking precision at LaserLaB VU. These measurements revealed a significant yet unexpected frequency shift that seems connected with the magnetic properties of one of the molecule’s nuclei, the deuteron.
Remarkably, a similar deuteron-related discrepancy was observed in precision measurements (performed elsewhere) of an exotic sibling of the hydrogen atom, muonic deuterium. These new high-precision measurements might thus have laid bare behavior of the deuteron in atoms and molecules that has previously been overlooked.
New physics?
The question is what causes the anomalous behavior. The experiments envisaged by Beyer and Koelemeij will try to provide an answer by precisely measuring and comparing the quantum properties of hydrogen molecular ions containing zero, one, or two deuterons (H2+, HD+, and D2+), and in various states of vibrational excitation. In this way, various potential explanations – be they shortcomings of the theoretical description, shortcomings of previous experiments, or possible manifestations of new physics beyond the standard model of particle physics – can be independently tested. The experiments will be carried out in existing as well as new setups, exploiting the precision measurement infrastructure of the QMLA group.
Image: Picture of the ion trap that will be used in the experiments. This ion trap is kept in an ultrahigh vacuum, and contains about 100 HD+ molecules (see inset). To read out their magnetic properties, the HD+ molecules are embedded in an extremely cold crystal consisting of about 1500 ions of the element beryllium (Be+), who themselves are being cooled and read out with the help of an ultraviolet (UV) laser beam.