Observation of a triplet structure in d-wave Feshbach resonances

A d-wave Feshbach resonance between the $^{85}$Rb$|2, -2\rangle$+$^{87}$Rb$|1, -1\rangle$ scattering channel is observed in a mixture of ultracold $^{85}$Rb and $^{87}$Rb atoms. Analogous to the well-known doublet splitting of the p-wave resonance in $^{40}$K [1], we find a triplet structure originating from the magnetic dipole-dipole interaction between the valence electron spins of the two heteronuclear atoms. The three components of the resonance are respectively associated with the partial wave projections onto the direction of the magnetic field being $m_{l}$=0, $|m_{l}|$=1 and $|m_{l}|$=2. Such an interpretation and our observations are well characterized using the semi-analytic multichannel quantum-defect theory [2]. This work opens up new possibilities of studying the anisotropy in d-wave interaction dominated physics. \vspace{3ex} \newline [1] C. Ticknor, C. A. Regal, D. S. Jin, and J. L. Bohn, Phys. Rev. A 69, 042712 (2004). \newline [2] Bo Gao, Phys. Rev. A 84, 022706 (2011).