Some Significant Relations in the Quantum Theory of Spectra

Paul M. Danehy, Roger L. Farrow

We report detailed measurements of transition line shapes of degenerate four-wave mixing in the A2Σ+(υ′ = 0) ← X2Π(υ″ = 0) band of nitric oxide. We compared spectra obtained under conditions in which either population or thermal gratings were significant. Under conditions in which population gratings were significant, spectral lines were narrower and had intensities that varied more rapidly with the absorption B coefficient than in spectra dominated by thermal-grating scattering. In both cases we found excellent agreement with calculations that used perturbation theory to describe the population-grating contributions and the squared absorption spectra to describe the thermal-grating contributions. Our results show that quantitative prediction of degenerate four-wave mixing spectra requires relatively detailed knowledge of the ratio of contributions from the two mechanisms.

Niels Henrik David Bohr

Yunfei Wang, Huiying Du, Yuqing Li +5 more

Abstract The Feynman-Tan relation, obtained by combining the Feynman energy relation with the Tan’s two-body contact, can explain the excitation spectra of strongly interacting 39 K Bose-Einstein condensate (BEC). Since the shift of excitation resonance in the Feynman-Tan relation is inversely proportional to atomic mass, the test of whether this relation is universal for other atomic systems is significant for describing the effect of interaction in strongly correlated Bose gases. Here we measure the high-momentum excitation spectra of 133 Cs BEC with widely tunable interactions by using the second- and third-order Bragg spectra. We observe the backbending of frequency shift of excitation resonance with increasing interaction, and even the shift changes its sign under the strong interactions in the high-order Bragg spectra. Our finding shows good agreement with the prediction based on the Feynman-Tan relation. Our results provide significant insights for understanding the profound properties of strongly interacting Bose gases.

Will Salmon, Alessio Settineri, Salvatore Savasta +2 more

Emission spectra in the ultrastrong coupling regime are traditionally computed in a gauge-dependent theory. We present gauge-invariant spectra which show significant disagreement with previous results obtained using the standard quantum Rabi model.

G. M. Zhislin, A. Sigalov