Recently Koelemeij and colleagues obtained a very precise value of the proton-electron mass ratio through laser spectroscopy of molecules. However, the accuracy was limited by several factors, including limited knowledge of the magnetic interactions between the three particles that together form an HD+ molecule – the proton, the deuteron, and the electron. In their new research, the scientists will study these magnetic interactions with high precision using microwave fields. The results should therefore lead to a more precise value of the proton-electron mass ratio.
Extremely high measurement precision
The research of Koelemeij is aimed at high-precision measurements of the vibrations of molecules. In particular, he focuses on the molecular hydrogen ion, HD+. During a measurement, the molecular vibration is driven using advanced laser systems developed at LaserLaB VU. These lasers also allow measuring the frequency at which the HD+ molecules vibrate to very high precision. “In fact, the measurement precision is so high – just a few parts per trillion – that a dedicated atomic clock is needed as a frequency reference”, Koelemeij explains. “To achieve very pure vibrations, the HD+ molecules are stored under vacuum in an ion trap filled with laser-cooled atomic beryllium ions to cool them to a very low temperature.”
The results will also help answer the question why especially the deuteron seems to behave differently than theory predicts. According to Koelemeij this might be caused by shortcomings of the present theory, or even by new particles or forces of nature that so far have eluded detection. Currently, experiments are conducted in labs around the world – including several experiments in the Quantum Metrology and Laser Applications group at the VU Department of Physics and Astronomy – that are designed to detect or rule out possible manifestations of such ‘new physics’.
Precision Measurement Grant
The National Institute of Standards and Technology is a scientific agency of the United States federal government. With the NIST Precision Measurement Grant Program the agency supports significant research in the field of fundamental measurement or the determination of fundamental constants. Since the start of the program in 1970, NIST has awarded two grants each year.