Deterministic loading of molecular arrays by microwave-assisted collisions

Optical tweezer arrays are a powerful platform for quantum simulation and computing. While atomic arrays have achieved near-unity filling fractions through techniques like light-assisted collisions, these methods do not translate directly to molecules. Molecular collisions at short range typically result in universal loss, preventing the controlled energy release required to eject excess particles. This paper addresses this challenge by proposing a new mechanism: microwave-assisted collisions (MWACs).

The authors introduce a strategy to suppress short-range loss by shelving molecules in rotationally or vibrationally excited states. This creates a repulsive van der Waals interaction that prevents molecules from reaching the short-range regime where uncontrolled loss occurs. By applying a microwave field, the researchers can dress these rotational states, creating a resonant dipole-dipole interaction. This allows for a controlled collision where a precise amount of energy (determined by the microwave detuning) is released, enabling the deterministic ejection of one of the two molecules in a tweezer.

The proposed scheme follows a cycle: loading molecules into the tweezers, applying the microwave-assisted collision to trigger energy release, ejecting the excess molecule, and shelving the remaining molecule into a protected state. Using CaF as a model system, the authors performed coupled-channels scattering calculations to quantify the efficiency of these collisions. They demonstrate that by utilizing rotational van der Waals repulsion, filling fractions of up to 87% are achievable. By leveraging even stronger ro-vibrational van der Waals repulsion, the predicted filling fraction increases to 96%, limited primarily by the lifetime of the vibrationally excited state.