Molecular Laser-Cooling in a Dynamically Tunable Repulsive Optical Trap

TL;DR

This paper demonstrates laser cooling of CaF molecules in a repulsive optical trap with suppressed AC Stark shifts, enabling efficient transfer from magneto-optical traps and maintaining low temperatures.

Contribution

It introduces a dynamically tunable repulsive optical trap for molecules, achieving near-lossless transfer and effective in-trap cooling, advancing molecular trapping techniques.

Findings

Suppressed AC Stark shifts in repulsive traps.

Effective $b1$-enhanced gray molasses cooling inside the trap.

High transfer efficiency from magneto-optical to optical traps.

Abstract

Recent work with laser-cooled molecules in attractive optical traps has shown that the differential AC Stark shifts arising from the trap light itself can become problematic, limiting collisional shielding efficiencies, rotational coherence times, and laser-cooling temperatures. In this work, we explore trapping and laser-cooling of CaF molecules in a ring-shaped repulsive optical trap. The observed dependences of loss rates on temperature and barrier height show characteristic behavior of repulsive traps and indicate strongly suppressed average AC Stark shifts. Within the trap, we find that $\Lambda$-enhanced gray molasses cooling is effective, producing similar minimum temperatures as those obtained in free space. By combining in-trap laser cooling with dynamical reshaping of the trap, we also present a method that allows highly efficient and rapid transfer from molecular magneto-optical traps into conventional attractive optical traps, which has been an outstanding challenge for experiments to date. Notably, our method could allow nearly lossless transfer over millisecond timescales.