A High-Flux Source of Cold Strontium with a Loading Rate of $4 \times 10^{10}$ atoms/s for Open Release

Abstract

We present a high-flux source of cold strontium atoms based on a two-dimensional magneto-optical trap (2D MOT) and a Zeeman slower. We use the source to load a 3D MOT in a separate science chamber, observing a loading rate of $4 \times 10^{10}$ atoms/s -- to our knowledge, the highest reported loading flux for strontium. To characterise the vacuum pressure in the science chamber, we load the atoms into a magnetic trap and measure a lifetime of between 8 and 24 seconds, depending on oven temperature. Finally, we characterise the atom flux and velocity distributions from the oven and from the 2D MOT source, finding reasonable agreement with models in the free molecular flow regime. Our results show it is possible to readily produce a cold strontium flux at comparable levels to alkali species, at oven temperatures compatible with long-term operation, and at vacuum pressures suitable for state-of-the-art quantum experiments. We make our design available at no cost, to benefit researchers in the quantum community.

Figures (10)

• Figure 1: (a) Vacuum system and mounting frame. Some of the 2D MOT optics are shown mounted to the source chamber limbs. The full enclosure forms a full cuboid (670 mm (W) $\times$ 600 mm (D) $\times$ 545 mm (H)) enclosing the chamber, but the top and front faces are not shown here. (b) Source chamber as viewed from the science chamber, showing the location of the magnet assemblies and orientation of the 2D MOT and Zeeman slowing beams. (c) Top view of the vacuum system showing the orientation of the push, Zeeman slowing, oven fluorescence and plug beams used for flux characterisation (see text). (d) Side view of the vacuum system showing the orientation of the probe beam used for flux characterisation in the science chamber.
• Figure 2: Simulated trajectories of atoms along the axis of the Zeeman slower. Upper and lower are without and with Zeeman slower magnets and beam. The heatmap shows the acceleration of the atoms at each position and velocity on a symmetric logarithmic scale, relative to the maximum acceleration $a_{\rm max}$ (see \ref{['sec:zeeman-slower-simulations']}) from the $\sigma^+$ and $\sigma^-$ polarised slowing light and MOT beams. Each line is a simulated atom trajectory, with 20 trajectories shown on each plot. Black trajectories are those which are captured by the MOT, grey are those which escape. Below each simulation plot is the calculated transverse field profile along the oven axis.
• Figure 3: Transverse absorption spectrum of the atomic beam from the oven for a range of oven temperatures. The points are experimental data, the solid line is a fit to the model described in the text.
• Figure 4: (a) Top view of the science chamber showing the orientation of the plug beam, probe beam (propagating vertically), collection lenses and photodiode (PD). The black arrow shows the direction in which the atoms propagate. (b) Fluorescence signal used to determine atomic flux. Scatter from the plug beam can be seen up until the light is switched off a $t = 0$ ms. The signal increases as atoms enter the probe region. The region shaded in red is used to generate the curves in panel (c). (c) Example velocity distributions of atoms arriving into the detector region for various push beam intensities. (d) Most probable velocity of atoms reaching the second chamber (filled circles) as a function of push beam intensity, along with the total useful flux (open circles), calculated by integrating the velocity profiles up to 30 ms$^{-1}$.
• Figure 5: 3D MOT loading curves for a range of oven temperatures. The points are experimental data, the solid lines are fits to the exponential loading model. The inset shows the full loading curves, with the black dashed line indicating the 0.9e9atom cutoff used for fitting. Uncertainties are standard errors on the mean of 13 measurements.