Abstract
The multichannel Na-Cs interactions are characterized by a series of measurements using two atoms in an optical tweezer, along with a multichannel quantum defect theory (MQDT). The triplet and singlet scattering lengths are measured by performing Raman spectroscopy of the Na-Cs motional states and least-bound molecular state in the tweezer. Magnetic Feshbach resonances are observed for only two atoms at fields which agree well with the MQDT. Our methodology, which promotes the idea of an effective theory of interaction, can be a key step towards the understanding and the description of more complex interactions. The tweezer-based measurements in particular will be an important tool for atom-molecule and molecule-molecule interactions, where high densities are experimentally challenging and where the interactions can be dominated by intra-species processes.
Highlights
Tuning interactions in ultracold gases of atoms and molecules via Feshbach resonances or optical lattices have enabled studies of many rich quantum phenomena such as the BEC-BCS crossover [1], superfluid-to-Mott insulator transitions [2], and supersolidity [3,4,5]
With Na-Cs interactions completely characterized at a low magnetic field, we use our two-scale multichannel quantum defect theory (MQDT) to guide a search of Feshbach resonances at much higher magnetic fields
The agreement of the Feshbach resonance locations with the two-scale MQDT model combined with a series of tweezer-based measurements represents an important validation of the use of effective theory for interactions
Summary
Tuning interactions in ultracold gases of atoms and molecules via Feshbach resonances or optical lattices have enabled studies of many rich quantum phenomena such as the BEC-BCS crossover [1], superfluid-to-Mott insulator transitions [2], and supersolidity [3,4,5]. Probing two- to few-body interactions in cold atoms has traditionally been performed by scattering experiments in bulk gases [12] or by spectroscopy in optical lattices [13,14,15,16,17], both. Would measurements performed on two particles in an optical tweezer be sufficient to fully characterize two-body interaction, including the identification of Feshbach resonances? The single-scale MQDT [11,34,35,36,37] describes low-energy alkali-metal interactions with the fewest parameters by separation of the longrange potential −C6/r6 [with length scale β6 = (2μC6/h2)1/4] from the short-range potential, which is captured by the singlet and triplet scattering lengths. Whereas traditional bulk-gas and optical lattice experiments require suitable collisional properties (including miscibility) between all species in order to obtain a high phase-space density, the tweezer method instead achieves a high phase-space density by optically cooling individual particles [22,23,24,26] before merging them together
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