Observation of Persistent Flow of a Bose-Einstein Condensate in a Toroidal Trap

We have observed the persistent flow of Bose-condensed atoms in a toroidal trap. The flow persists without decay for up to 10 s, limited only by experimental factors such as drift and trap lifetime. The quantized rotation was initiated by transferring one unit of the orbital angular momentum from Laguerre-Gaussian photons to each atom. Stable flow was only possible when the trap was multiply connected, and was observed with a Bose-Einstein condensate fraction as small as 20%. We also created flow with two units of angular momentum and observed its splitting into two singly charged vortices when the trap geometry was changed from multiply to simply connected.

Figure 1

(a) Toroidal trap from the combined potentials of the TOP trap and Gaussian plug beam. (b) In situ image of a BEC in the toroidal trap. (c) TOF image of a noncirculating BEC released from the toroidal trap. (d) TOF image of a circulating BEC, released after transfer of $\hslash$ of OAM.

Figure 2

Survival probability of circulation as a function of trapping time in the TOP trap without the plug beam (circles) and with the plug beam (squares). Each data point is an average of 5–10 measurements. Inset: survival probability for 0.5 s trapping time, as a function of the voltage applied to external shim coils to displace the TOP trap center.

Figure 3

Survival probability for a 2 s trapping time, as a function of the maximum height of the plug beam optical potential, $V_0$ (normalized to the chemical potential, $\mu$).

Figure 4

Survival probability of a circulating BEC for a 2 s trapping time, as a function of the BEC fraction. Inset: three TOF images of a circulating BEC for BEC fractions of 24%, 15%, and 12%.

Figure 5

TOF pictures of doubly charged flow, initially stabilized for 0.5 s in the toroidal trap, for different holding times (4, 214, and 404 ms) in just the TOP trap.