Two-dimensional quantum gas in a hybrid surface trap

We demonstrate the realization of a two-dimensional (2D) quantum gas in a smooth optical surface trap. Using a combination of evanescent wave, standing wave, and magnetic potentials, we create a long-lived quantum gas deep in the 2D regime at a distance of a few microns from a glass surface. To realize a system suitable for many-body quantum simulation, we introduce methods such as broadband “white” light to create evanescent and standing waves to realize a smooth potential with a trap frequency aspect ratio of 300:1:1. We are able to detect phase fluctuations and vortices, and we demonstrate cooling to degeneracy and low disorder in the 2D configuration.

Figure 1

(Color online) Hybrid trap. (a) The trap is based on a dielectric surface formed by the superpolished horizontal bottom face of a fused silica substrate. Fused to the top of the substrate is a hemispherical lens with lateral planar facets which is designed to be part of a high numerical aperture imaging system. Three potentials form the trap: an EW beam from the top generates an exponential repulsive potential (red dash-dotted lines). A beam reflected off the bottom side of the surface creates a standing wave (SW, blue dotted lines). A parabolic magnetic trap (green dashed lines) provides an upwards force and lateral confinement. (b) Schematic of magnetic trap potential with BEC closely below surface. The black line denotes the combined potential. (c) Evanescent wave configuration loaded by shifting the magnetic trap minimum inside the glass generating confinement between the magnetic gradient and the evanescent wave. (d) Atoms loaded into single plane of SW trap, $1.5\mu \text{m}$ from the surface. The trap provides deep 2D confinement with lateral trap frequencies of $2\pi \times 20\text{Hz}$ and a vertical confinement of $2\pi \times 5.9\text{kHz}$.

Figure 2

(Color online) (a) Moving the atoms against the surface without EW leads to a sudden loss (red circles), which is avoided by the repulsive potential (blue filled circles). (b) Atom lifetime in the hybrid EW trap, red line corresponds to fit with single exponential.

Figure 3

(Color online) Quantum gas deep in 2D regime. Time of flight images from standing wave trap: (a) the vertical density profile is Gaussian, showing that the system is deep in the 2D configuration. In the lateral direction, it is well described by a bimodal Thomas-Fermi profile with $\approx 20\%$ thermal fraction in this case: (b) integrated lateral profile averaged over 86 samples and (c) density fluctuations caused by thermal 2D phase fluctuations in single profile from same data set (inset shows $140\mu \text{m}\times 280\mu \text{m}$).

Figure 4

(Color online) Loading of single and multiple planes in the standing-wave trap. (a) atoms loaded into a single site, imaged from the side after release and 17 ms time-of-flight, and (b) interference between atoms from two planes. (c) Interference pattern between two planes at a higher temperature showing the presence of a thermally activated vortex. (d) The vertical density profile obtained by rf addressing shows the occupation of two planes. The red line denotes a two-peak Lorentzian fit, which yields a peak separation of $1.51\pm 0.06\mu \text{m}$.