Figure 1

Experimental schematic. Atoms were confined in a gravitomagnetic trap [19] with trap frequencies ranging from $2\pi \times (2,2,6.5)\mathrm{H}\mathrm{z}$ to $2\pi \times (11,11,6.5)\mathrm{H}\mathrm{z}$, near a $\sim 20\mu \mathrm{m}$ thick Si surface. (a) Quantum reflection was studied by inducing a dipole oscillation of amplitude $A$ perpendicular to the surface and centered on the surface. The incident velocity was varied from $1–8\mathrm{m}\mathrm{m}/\mathrm{s}$ by adjusting $A$. (b) Atoms were loaded into a surface trap with zero incident velocity using an intermediate trap located at $A/2$. Atoms initially confined at a distance $A$ from the surface were made to undergo a dipole oscillation of amplitude $A/2$ by shifting the trap center halfway to the surface. After holding for half a trap period, $T_{\perp }/2$ , the atoms were incident on the surface with near zero velocity. The trap center was again shifted by $A/2$ towards the surface, trapping the atoms against the Si wafer. To ensure contact between atoms and the surface, the center of the final trap was located $\sim 10\%$ of the original condensate size beyond the Si surface.Reuse & Permissions

Figure 2

Atoms reflecting from a Si surface. Atoms confined $\sim 70\mu \mathrm{m}$ from a Si surface were transferred into a harmonic trap centered on the surface with $2\pi \times (3.3,2.5,6.5)\mathrm{H}\mathrm{z}$. The dipole oscillation of the condensate was interrupted periodically by collisions with the surface, which reversed the cloud’s center of mass velocity. After a variable hold time, atoms were released from the trap, fell below the edge of the surface and were imaged with resonant light after 26 ms time of flight. The position of the atoms in time of flight is the sum of the in-trap position at the time of release and the product of the release velocity and time of flight. (a) Time-of-flight images of atoms after increasing hold times show the partial transfer of atoms from the initial condensate (right) into the reflected cloud (left) as the collision occurs. The separation is due to the reversed velocity. The vertical line shows the horizontal location of the surface. The field of view is 1.4 mm wide. (b) The time-of-flight positions of the incident and reflected atom clouds relative to the surface are well modeled by a single particle undergoing specular reflection in a half harmonic trap (solid line). During collision, the behavior deviates from the single particle model because of the finite cloud diameter of $\sim 60\mu \mathrm{m}$. A second reflection is visible at 270 ms.Reuse & Permissions

Figure 3

Reflection probability vs incident velocity. Data were collected in a magnetic trap with trap frequencies $2\pi \times (3.3,2.5,6.5)\mathrm{H}\mathrm{z}$. Incident and reflected atom numbers were averaged over several shots. Vertical error bars show the standard deviation of the mean of six measurements. Horizontal error bars reflect the uncertainty in deducing $v_{\perp }$ from the applied magnetic field $B_{\perp }$. The solid curve is a numerical calculation for individual atoms incident on a conducting surface as described in the text.Reuse & Permissions

Figure 4

Lifetime in the Si surface trap. Solid (open) circles show the remaining atom fraction vs time for a $2\pi \times (9,9,6.5)$ [$2\pi \times (3.3,2.5,6.5)$] Hz trapping potential with an initial atom number $3\times {10}^4$ ($9\times {10}^4$). The solid line exponential fit gives a lifetime of 23 ms (170 ms) for the high (low) frequency trap geometry. The lifetime for atoms confined far from the surface exceeded 20 s for either geometry.Reuse & Permissions