Atom-number enhancement by shielding in a strontium magneto-optical trap

Atomic strontium has gained popularity over the last years in various fields of quantum science, such as quantum simulation and computation, atomic clocks and atom interferometers. Many of these applications require the preparation of laser-cooled clouds with large atom numbers. In this talk, we report on a method to double the atom number in a strontium magneto-optical trap (MOT) that can benefit existing experiments as it requires no constructional changes.

The method consists in driving the narrow red intercombination line at 689nm (¹S₀ →³P₁) on resonance during the blue MOT operated on the broad-linewidth transition ¹S₀ → ¹P₁ at 461nm. As a result, we populate a short-lived reservoir state that is shielded from losses arising in the MOT cooling cycle. This shielding leads to the observed atom-number enhancement in the steady-state. Our result persists in the presence of repumping lasers, and holds for all the stable strontium isotopes. The atom-number enhancement is preserved through the subsequent stages of the cooling and has boosted our efficiency for preparing strontium-84 Bose-Einstein condensates. As an outlook, we will discuss the progress of loading the condensate into a two-dimensional optical lattice and realizing a strontium quantum-gas microscope.