Bose-Einstein Condensation of ${}^{84}\mathrm{Sr}$

We report Bose-Einstein condensation of ${}^{84}\mathrm{Sr}$ in an optical dipole trap. Efficient laser cooling on the narrow intercombination line and an ideal $s$-wave scattering length allow the creation of large condensates ($N_0\sim 3\times {10}^5$) even though the natural abundance of this isotope is only 0.6%. Condensation is heralded by the emergence of a low-velocity component in time-of-flight images.

Figure 1

Timing diagram for principal experimental components. The traces are offset for clarity and heights schematically indicate variation in power. Note the break in the time axis.

Figure 2

Number, temperature, and phase space density along a typical evaporation trajectory, from 200 ms after the completion of loading of the optical dipole trap and commencement of evaporation, until quantum degeneracy is reached 3 s later. The phase space density increases by a factor of 100 for a reduction of atom number by a factor of 3.

Figure 3

Appearance of Bose-Einstein condensation in absorption images (left) and areal density profiles (right). Data correspond to 35 ms of free expansion after indicated evaporation times, $t$. (left) Images are $780\mu \mathrm{m}$ per side, and have the same time stamp as the density profiles. (right) The areal density profiles are from a vertical cut through the center of the atom cloud, and temperatures are extracted from 2D Gaussian fits to the thermal component. At 3.0 and 3.6 s, a bimodal distribution indicative of Bose-Einstein condensation becomes increasingly clear, and then a pure condensate is shown at 4.35 s.

Figure 4

Condensate radius after release from the trap. The expansion of the condensate is fit by the Castin-Dum model [Eq. (3)] assuming trap parameters obtained from profiling the ODT beam and measuring the trap oscillation frequencies. Deviations at early times most likely reflect limitations of the optical imaging system and large optical depth of the condensate.

Figure 5

Number of condensate atoms held in the optical dipole trap at constant depth versus time after the evaporation (see text). The solid line is an exponential fit to the data, yielding a condensate lifetime of $8\pm 1\mathrm{s}$.