Ultrahigh finesse cavity-enhanced spectroscopy for accurate tests of quantum electrodynamics for molecules

Abstract

We report the most accurate measurement of the position of the weak quadrupole S(2) 2-0 line in D2. The spectra were collected with a frequency-stabilized cavity ring-down spectrometer (FS-CRDS) with an ultra-high finesse optical cavity (F = 637 000) and operating in the frequencyagile, rapid scanning spectroscopy (FARS) mode. Despite working in the Doppler-limited regime, we reached 40 kHz of statistical uncertainty and 161 kHz of absolute accuracy, achieving the highest accuracy for homonuclear isotopologues of molecular hydrogen. The accuracy of our measurement corresponds to the fifth significant digit of the leading term in QED correction. We observe 2.3σ discrepancy with the recent theoretical value. * mzab@doktorant.umk.pl † piotr.wcislo@fizyka.umk.pl

Sub-ppb Measurement of a Fundamental Band Rovibrational Transition in HD

“…The present result agrees with all previous values but shows a much smaller uncertainty. Interestingly, we note that six other measurements of hydrogen vibrational transition frequencies [5,7,8,[12][13][14], covering all three stable isotopologues, show fractional deviations from the theoretical predictions from H2Spectre consistent with the 8.7 × 10 −9 deviation measured here to within experimental uncertainty.…”

“…Because these transitions can be predicted with high precision using ab initio theory, comparisons between theory and experiment can be used to test quantum electrodynamics, search for new forces beyond the standard model, and determine the proton-electron and deuteron-electron mass ratios more precisely [1][2][3][4]. In recent years, many precise measurements of molecular hydrogen transition frequencies have been published [5][6][7][8], with some recent works reporting fractional uncertainties of less than one part-per-billion (ppb, 10 −9 ) on vibrational overtone and electronic transition frequencies [4,[9][10][11][12][13]. Many of these recent experiments (with a few notable exceptions [6,9]) detect infrared absorption by hydrogen in a gas cell.…”

Accurate deuterium spectroscopy and comparison with ab initio calculations

“…Experiment [15] Theory [15] Experiment (this work) Theory [2,3] - also observed for different kind of experiments on all stable hydrogen isotopologues [30,[32][33][34][35]. The reason for this discrepancy has not yet been clarified.…”

Transition frequencies in the (2-0) band of D2 with MHz accuracy

“…Nevertheless, the latest calculations [4] show a better agreement (1 MHz difference instead of 4 MHz [22]) with these combined experimental values and a reduced uncertainty (0.75 MHz [4] instead of 1.25 MHz [22]). The Torun group has recently remeasured the same transition with an improved accuracy of 160 kHz with a frequencystabilized cavity ring-down spectrometer in the frequency agile, rapid scanning spectroscopy (FARS) mode [26]. This most recent value shows a larger difference of 1590 kHz (~5.3×10 -5 cm -1 ) compared to the theoretical value of Ref.…”

“…[20] and in this work are marked with red dots, blue stars and green circles, respectively. The S(2) transition (square) was studied in Refs [21,22] and very recently in [26].…”