Nonlinear effect of cold Cs2 molecular conversion from ultracold atoms in a tunneling four-level structure

Due to the inevitability of the nonlinear collision between the particles in the experiment of the ultracold atomic condensates, it is of great significance to study the nonlinear effect for producing the ultracold molecules from the atomic condensates. In this work, we investigate theoretically the nonlinear effect induced by the two-body collision for producing ultracold Cs2 molecules from ultracold atoms by the stimulated Raman adiabatic passage in a tunneling four-level structure. Under the two-photon resonance condition and the coherent population trapping state, the conversion efficiency is influenced significantly by the nonlinear parameter. Meanwhile, the optimized parameter ranges of the resonance tunneling strength at the unstable excited molecular states, the effective Rabi frequencies of the two-laser fields and the detuning of pump field for different nonlinear parameter are suggested to obtain the high conversion efficiency of ground Cs2 molecules. At last, the maximum conversion efficiency up to 88.56% can be realized in the optimized parameter ranges.

Generalization of the Kutta–Joukowski theorem for the hydrodynamic forces acting on a quantized vortex

The hydrodynamic forces acting on a quantized vortex in a superfluid have long been a highly controversial issue. A new approach, originally developed in the astrophysical context of compact stars, is presented to determine these forces by considering small perturbations of the asymptotically uniform flows in the region far from the vortex in the framework of Landau–Khalatnikov two-fluid model. Focusing on the irrotational part of the flows in the Helmholtz decomposition, the classical Kutta–Joukowski theorem from ordinary hydrodynamics is thus generalized to superfluid systems. The same method is applied to predict the hydrodynamic forces acting on vortices in cold atomic condensates and superfluid mixtures.