Narrow Results

We show that it is possible to model two-body resonant interactions at low energy with a class of finite-range potentials based on the methods of Jost and Kohn. These potentials are expressed in terms of the effective range $r_0$ and the $s$-wave scattering length $a_s$. We derive continuum solutions of these potentials. By writing $V_{\pm }(r)=V_0(r)+V_{\pm }^{ϵ}(r)$, where the sign $+(-)$ refers to positive(negative) scattering length, $V_0(r)$ is of the form of Pöschl–Teller potential and $V_{\pm }^{ϵ}$ is expressed as a power series of the small parameter $ϵ={(\sqrt{1-2r_0/a_s})}^{-1}-1$ when $a_s$ is large, we derive Green’s function of $V_0(r)$. Using the Green’s function, solutions of $V_{\pm }(r)$ for $\left|a_s\right|\gg r_0$ can be obtained numerically by treating $V_{\pm }^{ϵ}(r)$ as a perturbation. We describe the threshold behavior of scattering phase shift for $V_0(r)$. This study may be important for developing a better understanding of physics of strongly interacting ultracold atomic gases with tunable interactions.

One of the many important contributions of Alex Dalgarno to Atomic, Molecular, and Optical (AMO) Physics relates to his work on ultracold physics. After a brief review of his early work on photoassociation (PA) of ultracold atoms and the formation of ultracold molecules, a short description of new results using Feshbach Optimized Photoassociation (FOPA) will be given. This research points to Alex's influence on the work now performed in my group at UConn.

We report on experiments exploring the physics of dipolar quantum gases using a ⁵²Cr Bose-Einstein condensate (BEC). By means of a Feshbach resonance, it is possible to reduce the effects of short range interactions and reach a regime where the physics is governed by the long-range, anisotropic dipole-dipole interaction between the large (6 µ_B) magnetic moments of Chromium atoms. Several dramatic effects of the dipolar interaction are observed: the usual inversion of ellipticity of the condensate during time-of flight is inhibited, the stability of the dipolar gas depends strongly on the trap geometry, and the explosion following the collapse of an unstable dipolar condensate displays d-wave like features.