Quasi-1D atomic gases across wide and narrow confinement-induced-resonances

We study quasi-one-dimensional atomic gases across wide and narrow confinement-induced-resonances (CIR). We show from Virial expansion that by tuning the magnetic field, the repulsive scattering branch initially prepared at low fields can continuously go across CIR without decay; instead, the decay occurs when approaching the non-interacting limit. The interaction properties essentially rely on the resonance width of CIR. Universal thermodynamics holds for scattering branch right at wide CIR, but is smeared out in narrow CIR due to strong energy-dependence of coupling strength. In wide and narrow CIR, the interaction energy of scattering branch shows different types of strong asymmetry when approaching the decay from opposite sides of magnetic field. Finally we discuss the stability of repulsive branch for a repulsively interacting Fermi gas in different trapped geometries at low temperatures.Comment: 7 pages, 4 figure

Universal Borromean Binding in Spin-Orbit Coupled Ultracold Fermi Gases

Borromean rings and Borromean binding, a class of intriguing phenomena as three objects are linked (bound) together while any two of them are unlinked (unbound), widely exist in nature and have been found in systems of biology, chemistry and physics. Previous studies have suggested that the occurrence of such a binding in physical systems typically relies on the microscopic details of pairwise interaction potentials at short-range, and is therefore non-universal. Here, we report a new type of Borromean binding in ultracold Fermi gases with Rashba spin-orbit coupling, which is {\it universal} against short-range interaction details, with its binding energy only dependent on the s-wave scattering length and the spin-orbit coupling strength. We show that the occurrence of this universal Borromean binding is facilitated by the symmetry of the single-particle dispersion under spin-orbit coupling, and is therefore {\it symmetry-selective} rather than interaction-selective. The state is robust over a wide range of mass ratio between composing fermions, which are accessible by Li-Li, K-K and K-Li mixtures in cold atoms experiments. Our results reveal the importance of symmetry factor in few-body physics, and shed light on the emergence of new quantum phases in a many-body system with exotic few-body correlations.Comment: 6+1.5 pages, 5 figures, published versio