Simple atomic systems are the ideal probe to test fundamental physics. For example, for hydrogen the 1S-2S transition frequency can nowadays be calculated with an impressive relative accuracy of 10$^{-12}$ [1], and measurements reach an even higher relative accuracy of 10$^{-15}$[2]. Combining different measurements in hydrogen has been used to determine fundamental constants such as the...
Precision spectroscopy of molecules promises a wealth of interesting applications e.g. for better determination of natural constants, for tests of fundamental particle theories, and for qubit realizations. Unfortunately, most molecules do not possess closed transitions for laser cooling, crucial for obtaining temperatures low enough for exploiting this novel realm of physics.
A way to...
The molecular hydrogen ion is a promising candidate for the metrology of fundamental constants, as its rovibrational transition frequencies can be calculated to the few-10$^{-12}$ accuracy level [1]. Measuring the transition frequencies between the levels with similar precision will provide an independent determination of the proton to electron mass ratio $m_p$/$m_e$ and possibly of the proton...
