Universal features for spin dipolar losses in atomic bose gases

Like elastic collisions, inelastic collisions provide exquisite information on interaction potentials. In an external magnetic field ($B$), spatially confined atoms can gain sufficient kinetic energies to escape due to spin flip inelastic collisions from magnetic dipole-dipole interaction (MDDI). This work reports combined experimental and theoretical studies of B-dependent loss lineshapes for ground state (F=1) $^{87}$Rb atoms in a Bose-Einstein condensate (BEC) with high atom number resolution. The measured loss rates are explained using wave functions from a semi-analytic quantum-defect theory (QDT) [1,2], which is consistent with numerical coupled-channel (CC) calculations. In the limit of large s-wave scattering length ($|a_s|$), the observed interesting features constitute a universal form with a ``dip" $B_\vee$ (for positive $a_s$) and a ``peak" $B_\wedge$ (for either positive or negative $a_s$) in the respective loss channels for one or two atom spin flips. The specific values of $B_\vee$ and $B_\wedge$ are determined predominantly by $a_s$ and also by the d-wave centrifugal barrier height $V_{l=2}$. \\\\ {[1] Gao, B, Phys. Rev. A 58, 1728 (1998); Phys. Rev. A 64, 010701(R) (2001); Phys. Rev. A 78, 012702 (2008).\\ {[2] Gao, B et al., Phys. Rev. A 72 042719 (2005).}}