Realizing quantum control and entanglement of particles is crucial for advancing both quantum technologies and fundamental science. Substantial developments in this domain have been achieved in a variety of systems1–5. In this context, ultracold polar molecules offer new and unique opportunities because of their more complex internal structure associated with vibration and rotation, coupled with the existence of long-range interactions6,7. However, the same properties make molecules highly sensitive to their environment8–10, affecting their coherence and utility in some applications. Here we show that by engineering an exceptionally controlled environment using rotationally magic11,12 optical tweezers, we can achieve long-lived entanglement between pairs of molecules using detectable hertz-scale interactions. We prepare two-molecule Bell states with fidelity \(0.92{4}_{-0.016}^{+0.013}\) , limited by detectable leakage errors. When correcting for these errors, the fidelity is \(0.97{6}_{-0.016}^{+0.014}\) . We show that the second-scale entanglement lifetimes are limited solely by these errors, providing opportunities for research in quantum-enhanced metrology7,13, ultracold chemistry14 and the use of rotational states in quantum simulation, quantum computation and as quantum memories. The extension of precise quantum control to complex molecular systems will enable their additional degrees of freedom to be exploited across many domains of quantum science15–17.
