Abstract
A saturation spectroscopy measurement of the P(1) line of the ($2-0$) band in HD is performed in a sensitive cavity-enhanced optical setup involving frequency comb calibration. The spectral signature is that of a Lamb-peak, in agreement with a density-matrix model description involving 9 hyperfine components and 16 crossover resonances of $\Lambda$-type. Comparison of the experimental spectra with the simulations yields a rovibrational transition frequency at 209,784,242,007 (20) kHz. Agreement is found with a first principles calculation in the framework of non-adiabatic quantum electrodynamics within 2$\sigma$, where the combined uncertainty is fully determined by theory.
Highlights
In this decade the hydrogen molecule has become a benchmark system for testing quantum electrodynamics (QED) and probing physics beyond the Standard Model [1]
Such tests can be accomplished by comparison between accurate measurements of, e.g., dissociation energies of the H2 molecule [2,3,4], with nonadiabatic calculations of the hydrogen molecule based on a four-particle variational framework and including relativistic and QED terms up to mα6 [5]
In conclusion we have demonstrated that the line shape as observed for the P(1) line in the (2-0) overtone band of HD can be described in terms of coherences between hyperfine substates
Summary
In this decade the hydrogen molecule has become a benchmark system for testing quantum electrodynamics (QED) and probing physics beyond the Standard Model [1]. A reanalysis at improved signal-to-noise ratio obtained with the NICEOHMS (noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy) technique by the Amsterdam team showed that the line shape appeared as dispersivelike [22] This phenomenon was explained as a result of the underlying hyperfine structure involving a large number of crossover resonances in the saturation spectrum. That was interpreted as a Fano line shape, caused by an interference between the rovibrational R(1) transition and an underlying continuum, reminiscent of the Fano line shape observed by the interference between transitions in the fundamental vibration of HD and broad collisionally induced continuum resonances [24] These discrepancies on transition frequencies and diverging explanations for the observed line shapes call for extended measurements, in particular since rovibrational transitions in the heteronuclear HD molecule, allow for extreme precision and constitute an excellent test ground for molecular QED
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