Rotational Coherence of Polar Molecules in an Optical Tweezer

An optical tweezer array of polar molecules is an appealing quantum computing platform. Qubit gate operations using rotational states are reliant upon dipolar interactions between individual molecules. We demonstrate a rotational qubit coherence time of \tau ~100 ms for laser cooled CaF molecules in an optical tweezer. Application of spin echo pulses result in a coherence time up to 500 ms. In order to achieve these long \tau, we engineer the anisotropic interaction of the molecules with the tweezer light. By tuning the tweezer light polarization and magnetic field to a “magic angle” condition, we reduce the differential polarizability and the inhomogeneous broadening due to the thermal motion of molecules in the trap. \tau could be increased with further cooling of the trapped molecule. \tau can be compared to dipolar gate times in this system, which are predicted to be on the microsecond to millisecond timescale. Thus, our observed 100 ms rotational coherence time is long enough to demonstrate the initial feasibility of this platform for quantum computing. We also note that the qubit states we use are generic to a large category of laser coolable molecules, including polyatomic species.