Observation of an inelastic feshbach resonance between individual ⁸⁷Rb and ³⁹K atoms in optical tweezers

An important route toward the preparation of cold molecules is magnetically tunable Feshbach resonances. Here we investigate an inelastic Feshbach resonance between a single pair of 87Rb and 39K atoms confined in an optical tweezer, with both atoms prepared in the |F=1,mF=−1⟩ state. By developing an in-situ imaging scheme for 39K, we directly measure magnetic-field-dependent collisional loss without separating the atoms after the interaction. For weak confinement, the resonance position measured in our experiment differs from the bulk-gas experiments. In contrast, we observe a significant shift of the resonance toward higher magnetic fields as the tweezer trap depth increases. Coupled-channel calculations accounting for finite temperature effects fail to explain the magnitude of this shift, suggesting that it originates from differential optical responses of the open-channel atom pair and the weakly bound molecular state under strong confinement. Our results indicate that optical tweezer light can significantly modify Feshbach resonance properties, opening a pathway toward optical control of atom–atom interactions and weakly bound molecular states in dual-species tweezer platforms.