Guided transport of ultracold gases of rubidium up to a room-temperature dielectric surface

Abstract

Part of Focus on Modern Frontiers of Matter Wave Optics and Interferometry: We report on the guided transport of an atomic sample along an optical waveguide up to a room-temperature dielectric surface. The technique exploits a simple hybrid trap consisting of a single beam dipole trap positioned ~125 μm below the field zero of a magnetic quadrupole potential. Transportation is realized by applying a moderate bias field (<12 G) to displace the magnetic field zero of the quadrupole potential along the axis of the dipole trap. We use the technique to demonstrate that atomic gases may be controllably transported over 8 mm with negligible heating or loss. The transport path is completely defined by the optical waveguide and we demonstrate that, by aligning the waveguide through a super polished prism, ultracold atoms may be controllably delivered up to a predetermined region of a surface. GENERAL SCIENTIFIC SUMMARY Introduction and background. There are still many open questions regarding the possibility of short-range corrections to gravity, which extend beyond the standard model. Historically, attempts to probe this force have covered length scales from the astronomical to the sub-millimetre. The results of such experiments are not only of fundamental significance, but also have important technological implications. In recent years, the rapid growth of cold atom experiments and their application to atom–surface measurements has opened up the possibility of pushing the measurement of short-range forces into a new regime of length scales below 10 μm. Main results. Common to all new atomic physics experiments aiming to probe gravity at short length scales is the need to controllably manipulate ultracold atoms near a room-temperature surface. Here we report the development of a new apparatus designed to study such atomic samples in close proximity to a super-polished surface of a dielectric Dove prism. Using a combined optical and magnetic trap we are able to deliver ultracold atomic samples up to the test surface precisely from distances of several millimetres with negligible heating or loss. Closer to the surface, we observe atom loss from the trap due to a truncation of the trapping potential resulting from the Casimir–Polder potential. We exploit this reduction in trap depth to reach degeneracy of the atomic sample. Wider implications. Our method of ultracold atom delivery is well suited to the loading of tightly confining surface traps of interest to many groups. The approach is simple to implement and extends the toolkit of techniques required to make precision measurements of short-range atom-surface interactions.