Final Report Summary - MOLFOUNTAIN (Precision measurements on cold molecules in a fountain)
The main achievements of this project are (i) further development of techniques to cool and trap molecules, particularly, demonstrating a method to load molecules from a beam into a trap with significantly reduced losses compared to previous work (Quintero-Pérez et al, Physical Review Letters 2013). (ii) a breakthrough in the understanding of how transitions in poly-atomic molecules depend on the fundamental constants (Jansen et al, Physical Review Letters 2011) – resulting in the most stringent test of a possible time-variation of these constants using astrophysical observations of methanol in the early universe (Bagdonaite et al, Science 2013).
Molecular spectroscopy is eminently suitable for performing tests of fundamental physics tests. The sensitivity of a spectroscopic experiment that searches for an energy shift due to a certain physical phenomenon depends on the accuracy of the measurements and on the inherent sensitivity of the transition to the effect one is looking for. Ultimately, the precision of any spectroscopic measurement is limited by the interaction time between the particle and the light field. By using cold, and therefore slow molecules, this interaction time can be increased.
In this project, we have tested a scheme to create a molecular fountain using Stark deceleration in combination with electrostatic lenses. Although we were unable to demonstrate a fountain we have developed a more efficient way to load molecules from a beam into a trap, and have been able to demonstrate very long interaction times, both in a slow beam and in the trap. Another goal of this project was to identify molecules that are suitable for testing the time-variation of the proton-to-electron mass ratio. We have found transitions in methanol molecules that have a ten to hundred fold increased sensitivity compared to ordinary rotational transitions. Methanol is one of the simplest molecules that exhibits internal rotation; the methyl (CH3) group rotates with respect to the alcohol (OH) group. In addition, the molecule rotates as a whole. We found that microwave transitions that convert the internal rotation to overall rotation – and vice versa – are very sensitive to the proton-to-electron mass ratio. Together with radio-astronomers of the MPG in Bonn, we have used astrophysical observations of methanol in the early universe to set the most stringent constraint of a possible time-variation of the fundamental constants (Bagdonaite et al, Science 2013).
Molecular spectroscopy is eminently suitable for performing tests of fundamental physics tests. The sensitivity of a spectroscopic experiment that searches for an energy shift due to a certain physical phenomenon depends on the accuracy of the measurements and on the inherent sensitivity of the transition to the effect one is looking for. Ultimately, the precision of any spectroscopic measurement is limited by the interaction time between the particle and the light field. By using cold, and therefore slow molecules, this interaction time can be increased.
In this project, we have tested a scheme to create a molecular fountain using Stark deceleration in combination with electrostatic lenses. Although we were unable to demonstrate a fountain we have developed a more efficient way to load molecules from a beam into a trap, and have been able to demonstrate very long interaction times, both in a slow beam and in the trap. Another goal of this project was to identify molecules that are suitable for testing the time-variation of the proton-to-electron mass ratio. We have found transitions in methanol molecules that have a ten to hundred fold increased sensitivity compared to ordinary rotational transitions. Methanol is one of the simplest molecules that exhibits internal rotation; the methyl (CH3) group rotates with respect to the alcohol (OH) group. In addition, the molecule rotates as a whole. We found that microwave transitions that convert the internal rotation to overall rotation – and vice versa – are very sensitive to the proton-to-electron mass ratio. Together with radio-astronomers of the MPG in Bonn, we have used astrophysical observations of methanol in the early universe to set the most stringent constraint of a possible time-variation of the fundamental constants (Bagdonaite et al, Science 2013).