Hyperfine structure and superfluidity of molecular Bose-Einstein condensates

In our first work, we investigate the phase transformation from atomic to molecular Bose-Einstein condensates (BEC). Coupling between atoms and diatomic molecules can be expressed as a process of annihilating a molecule to create two atoms and vice versa. If we include the phase of the atomic and molecular wavefunctions into this exchange, the system will remain invariant as long as the phase of the molecular wavefunction is twice as that of the atomic wavefunction. To probe this phase doubling, we implement an interferometric technique utilizing vortices. Quantum vortices are characterized by the phase winding of the macroscopic wavefunction around the annulus. The phase of the vortex is doubled when we convert an atomic BEC containing a single vortex into a molecular one. To detect this phase transformation, we perform interferometry using an optical lattice to create interference fringes. The vorticity will affect the formation of the interference fringes.

In our second work, we explore the near-threshold hyperfine structure of Cs2 molecules. While molecular states near the lowest energy manifold are well understood, an experimental and theoretical picture of the molecular states near the f₁ = 3, f₂ = 4 manifold is still lacking. We discuss the results of spectroscopy experiments mapping g-wave states in this new regime and compare our results to coupled-channel scattering calculations to extract quantum numbers. The states identified in this work introduce new possibilities in the study of coherent, many-body chemistry by enabling precise state control of BEC of Feshbach molecules in various quasibound rotational and hyperfine states.