This project investigates strong interaction in ultracold atoms in a two-chamber vacuum system. In BEC chamber we study the tunable interaction in ultracold ⁸⁵Rb-⁸⁷Rb mixtures via Feshbach resonances. In Rydberg chamber we take advantage of the strong and controllable long-range interaction of Rydberg atoms to study strongly-correlated quantum systems such as quantum gates.

Recent results

Observation of broad p-wave Feshbach resonances in ultracold ⁸⁵Rb-⁸⁷Rb mixtures^[1]

Ultracold atoms with controllable interaction via Feshbach resonances (FRs) have provided an ideal system to study universal behaviors in few- and many-body physics. We apply the semi-analytic multichannel quantum-defect theory to predict and characterize FRs in ⁸⁵Rb-⁸⁷Rb mixtures. The mixture is predicted and observed to exhibit a rich spectrum of “broad” s-wave and p-wave FRs. Of particular interest, a very broad entrance-channel dominated p-wave resonance is identified, which brings exciting opportunities for investigating universal behaviors with strong coupling in nonzero partial waves.

We observe the Feshbach spectroscopy of the mixture at a temperature of 2μK in an optical dipole trap. The atom number is measured after ramping the magnetic field to a certain value and holding the mixture for some amount of time. The presence of FRs results in an enhanced atom loss due to the increase of the three-body recombination rate, and thereby shows up loss features in the spectrum as a function of the magnetic field. The essential elements of our experimental setup and the Feshbach spectrum for the ⁸⁵Rb|2, −2> + ⁸⁷Rb|1, −1> channel are shown in Figures below.

[1].  S. Dong, Y. Cui, C. Shen, Y. Wu, M. K. Tey, L. You, and B. Gao, Phys. Rev. A 94, 062702 (2016).

Observation of Broad d-Wave Feshbach Resonances with a Triplet Structure ^[2]

Two "broad" d-wave Feshbach resonances (FRs) from coupling between d waves in both the open and closed channels are discovered in an ultracold 85Rb-87Rb mixture. The d-wave nature of the resonances are proved by the observation of a triplet structure with a splitting ratio well explained by the perturbation to the closed channel due to interatomic spin-spin interaction. These tunable "broad" d-wave resonances, especially the one in the lowest-energy scattering channel, could find important applications in simulating d-wave coupling dominated many-body systems.

Figure (a) shows the spin-spin interaction induced level splitting in the closed channel according to the azimuthal quantum number ml, which explains the origin of the triplet structure of d-wave FRs. The experimentally measured loss spectra of a d-wave FR are shown in Figure (b)-(d), where the triplet structure is fully resolved at a temperature of 400nK.

[2].  Yue Cui, Chuyang Shen, Min Deng, Shen Dong, Cheng Chen, Rong Lü, Bo Gao, Meng Khoon Tey, and Li You, Phys. Rev. Lett. 119, 203402 (2017).
Editors Suggestion and Viewpoint article "Scattering Atoms Catch the d Wave" by Niels Kjærgaard, Physics 10, 123 (2017). DOI · PDF