Bose-Einstein condensate in a box

Bose-Einstein condensates have been produced in an optical box trap. This optical trap type has strong confinement in two directions comparable to that which is possible in an optical lattice, yet produces individual condensates rather than the thousands typical of a lattice. The box trap is integrated with single-atom detection capability, paving the way for studies of quantum atom statistics.

Figure 1

The crossed ${\mathrm{TEM}}_{01}$ beams $\left({\mathrm{xTEM}}_{01}\right)$ are shown pictorially on the left. The potential shapes of the trap are given in arbitrary units on the right. The potential, $U$, in the $x$ and $y$ directions have the shape of their respective ${\mathrm{TEM}}_{01}$ beams. The endcap beams produce a trap along the $z$ axis; the Gaussian walls are separated by $d=80\mu \mathrm{m}$. The endcaps are not shown on the left; gravity is down in the pictorial.

Figure 2

Designer blue beams. Above are CCD pictures of various beams imaged as on the atom cloud. (a) ${\mathrm{vTEM}}_{01}$ beam. (b) Endcap beam in a general setting showing 10 spots. (c) Endcap beam as in the ${\mathrm{xTEM}}_{01}$ trap of Fig. 1. (d) Compensation beam driven with seven frequencies. (e) Compensation beam with 80 frequencies.

Figure 3

(a) An absorption image of a BEC of $3\times {10}^3$ atoms in a box with Gaussian walls spaced by $80\mu \mathrm{m}$ along the $z$ axis. (b) The profile of the BEC along the $z$ axis integrated vertically. The image is in situ, where the absorption beam is turned on in addition to the optical trap. Resolution is limited by expansion during the $30\text{−}\mu \mathrm{s}$ exposure and the upper and lower stripes are imaging artifacts.

Figure 4

Absorption images of BECs in $80\text{−}\mu \mathrm{m}$ boxes. (a) $N\approx 2\times {10}^3$ without a compensation beam. The cloud shows a region of higher density to the right. (b) The same as (a) but with the addition of an appropriate compensation beam. (c) $N\approx 5\times {10}^2$ with a compensation beam averaged over 10 separate exposures. The color scale is different from that in Fig. 3.

Figure 5

Fluorescence signal for an atom transferred from the optical trap into the small MOT at time zero. The signal shows that a single initial atom is transferred and held for 2 s. The level changes afterwards are due to random loss and background loading. The inset is a fluorescence image of the single atom for a 1-s exposure from the beginning of this run.