Rotational Spectroscopy and Magic 3D Optical Lattices for Ultracold ⁶Li⁴⁰K Molecules

We report highly-resolved rotational spectroscopy of ultracold ⁶Li⁴⁰K molecules, search for the magic condition via b3Pi transition, and the extension of molecule coherence time in the magic 3D optical lattices.

We first present rotational spectroscopy of the J=1 hyperfine structure at 215.5 G. By analyzing transition frequencies to excited states, we extract hyperfine interaction constants. One stretched transition is further narrowed down to Hz-level resolution, and the coherence time in a 1070nm optical dipole trap is measured, with the coherence timescale of approximately 10 microseconds.



To extend the coherence time, frequency-dependent polarizability calculations for the ground and first rotational excited states of 6Li40K are conducted. Via spin-orbital coupling between a1Sigma and b3Pi, we found the transition of |b³Π, v=0, J=1> from ground state molecules at 314.2305 THz. We further experimentally calibrated the feature in the polarizability spectra, particularly in the vicinity of a broad and far-detuned magic wavelength where the differential light shift remains negligible across the trap. Magic points occur at -8.9 GHz (90 deg laser polarization) and +6.8 GHz (0 deg laser polarization) away from the nearest transition. At the magic points, polarizability change within 1kHz by varying laser intensity from 0 to 9 kW/cm². We further built up a 3D magic optical lattice. The fine tuning of the coherence optimization via magic frequency is ongoing.