Quantum-Correlated Frequency Shift in Photoassociation

Alexander Guttridge

Matt Mackie

We theoretically investigate the effect of anomalous quantum correlations on the light-induced frequency shift in the photoassociation spectrum of a Bose-Einstein condensate. Anomalous quantum correlations arise because, although formed from a pair of zero-momentum condensate atoms, a condensate molecule need not dissociate back to the atomic condensate, but may just as well form a noncondensate atom pair with equal and opposite momentum, i.e., due to rogue photodissociation. The uncorrelated frequency shift of the photoassociation spectrum is to the red and linearly dependent on the laser intensity I. In contrast, anomalous correlations due to rogue dissociation lead to a blueshifted photoassociation spectrum. For sufficiently low light intensities, the rogue blueshift is dominant and proportional to sqrt[I].

Jordan M. Gerton, Brian J. Frew, Randall G. Hulet

A light-induced frequency shift is observed in single-photon photoassociative spectra of magnetically trapped, quantum degenerate ${}^{7}\mathrm{Li}.$ The shift is a manifestation of the coupling between the threshold continuum scattering states and discrete bound levels in the excited-state molecular potential induced by the photoassociation laser. The frequency shift is observed to be linear in the laser intensity with a measured proportionality constant that is in good agreement with theoretical predictions. This phenomenon has important implications for a scheme to alter the interactions between atoms in a Bose-Einstein condensate using photoassociation resonances.

Alexander Guttridge

Randall G. Hulet

Wenliang Liu, Xiaofeng Wang, Jizhou Wu +6 more

We report on the experimental observation and quantitative determination of the laser-induced frequency shift (LIFS) of the ultracold polar molecules formed by photoassociation (PA). The experiments are performed by detecting a series of double PA spectra with a molecular hyperfine structure, which are induced by two PA lasers with a precise and adjustable frequency reference. We find that the LIFS of the molecular hyperfine levels shows a linear dependence on PA laser intensity.