Large magnetic storage ring for Bose-Einstein condensates

Cold atomic clouds and Bose-Einstein condensates have been stored in a $10\mathrm{cm}$ diameter vertically oriented magnetic ring. An azimuthal magnetic field enables low-loss propagation of atomic clouds over a total distance of $2\mathrm{m}$, with a heating rate of less than $50\mathrm{nK}∕\mathrm{s}$. The vertical geometry was used to split an atomic cloud into two counter-rotating clouds which were recombined after one revolution. The system will be ideal for studying condensate collisions and ultimately Sagnac interferometry.

Figure 1

(Color online) Four circular coils with average diameter $10\mathrm{cm}$ make up the storage ring (thin circle) to which the axial wire adds an adjustable azimuthal magnetic field. The square coils localize the atoms (small cigar) in either a magneto-optical or magnetic trap depending on the current direction in the right square coil pair.

Figure 2

(Color online) A Monte Carlo simulation of atomic dynamics in the vertically oriented storage ring for a $2\mathrm{\mu }\mathrm{K}$ initial cloud of atoms. Images (a) and (b) represent lossless atom dynamics for a cloud released at $\overline{{\theta }_0}=0$ and $\overline{{\theta }_0}=60\mathrm{mrad}$, respectively. The white lines mark the extent of our $110\mathrm{mrad}$ experimental viewing region.

Figure 3

(Color online) Experimental storage ring dynamics for $2\mathrm{\mu }\mathrm{K}$ atoms with (a) $B_{\theta }=0\mathrm{G}$ and (b) $B_{\theta }=10\mathrm{G}$. In (c), multiple revolutions of a BEC in a ring with $B_{\theta }=10\mathrm{G}$ are seen. Numbers denote time in ms, absorption images are $0.4\times 5.4{\mathrm{mm}}^2$.

Figure 4

The relative atomic population, $P\left(t\right)$, viewed by the CCD camera as a function of time for $2\mathrm{\mu }\mathrm{K}$ atoms. Experimental data with $B_{\theta }=0\mathrm{G}$ and $B_{\theta }=10\mathrm{G}$ are shown with circles and triangles, respectively. The relative Monte Carlo atomic population in the viewing region of Fig. 2a (dashed curve) and Fig. 2b (solid curve) are shown for comparison. Good quantitative agreement can be seen between the $B_{\theta }=10\mathrm{G}$ data and the Monte Carlo simulation of an atomic cloud released from ${\theta }_0=60\mathrm{mrad}$. The $B_{\theta }=0\mathrm{G}$ data only fit the expected dashed theoretical curve initially due to large Majorana losses.

Figure 5

(Color online) A BEC at the top of the ring was split into two counter-rotating clouds by the faster-than-harmonic circular potential. These split atomic clouds can be seen recombining here after one revolution in the ring. Times are in ms, each image is $150\times 3400\mathrm{\mu }{\mathrm{m}}^2$ and is taken after a $3\mathrm{ms}$ ballistic expansion. Fringes are, unfortunately, only due to our camera.