Degenerate 39K Bose gases in dynamic size-tuneable box traps

Homogeneous atomic clouds in optical box potentials have allowed novel experiments on phenomena such as the second sound, critical dynamics and turbulence, which are much harder, or in some cases impossible, to study in the more common harmonic traps, where the atomic density is inhomogeneous [1]. However, the production of box-trapped atomic gases has so far relied on an intermediate cooling step in harmonic traps. Extending the capabilities of box traps, we use electrically controlled focus-tuneable lenses to create optical boxes (for 39K atoms) whose size can be changed in real time. This allows for direct transfer of laser-cooled clouds into a box trap and runaway evaporation via independent control of the trap depth and the collision rate; moreover the initial conditions for evaporation can be improved by performing laser cooling on clouds already trapped in the dark box [2]. Beyond improving the production of homogeneous gases, the dynamically tuneable boxes open further possibilities for many-body experiments with degenerate gases, including studies of thermodynamics in dynamical containers and the attainment of high-density homogeneous gases that are favourable for experiments on collective light scattering [3]. We will give an overview of our first experiments with these novel traps.

[1] Navon, N., Smith, R.P. & Hadzibabic, Z. Quantum gases in optical boxes. Nat. Phys. 17, 1334–1341 (2021).

[2] Yukai Lu, Connor M. Holland, & Lawrence W. Cheu , Molecular Laser Cooling in a DynamicallyTunable Repulsive Optical Trap, Phys. Rev. Lett. 128, 213201

[3] Lu, YK., Margalit, Y. & Ketterle, W. Bosonic stimulation of atom–light scattering in an ultracold gas. Nat. Phys. (2022).