Long-lived multilevel coherences and spin-1 dynamics encoded in the rotational states of ultracold molecules.

Rotational states of ultracold polar molecules possess long lifetimes, microwave-domain coupling, and tunable dipolar interactions. The availability of numerous rotational states has inspired many applications, including simulating quantum magnetism, encoding high-dimensional qudits and generating large synthetic dimensions. However, engineering the coherent superpositions of multiple rotational states needed for these applications is difficult owing to strong differential light shifts. Here, we overcome this challenge using individual molecules confined in near-magic wavelength optical tweezers. Through precision Ramsey spectroscopy, we find the exact magic wavelengths and sensitivities to detuning errors for multiple rotational state superpositions. We find for traps polarised parallel to the quantisation axis, the magic wavelengths are closely clustered enabling long-lived coherence across multiple rotational states simultaneously. Using a generalised Ramsey sequence, we demonstrate second-scale coherent spin-1 dynamics encoded in three rotational states and perform multiparameter estimation. With modest experimental improvements, we predict second-scale coherence across ten rotational states is achievable.