Single-atom detection of calcium isotopes by atom-trap trace analysis

We demonstrate a combination of an isotopically purified atom beam and a magneto-optical trap which enables single-atom detection of all stable isotopes of calcium (40, 42, 43, 44, 46, and 48). These isotopes range in abundance from 96.9% $\left({}^{40}\mathrm{Ca}\right)$ to 0.004% $\left({}^{46}\mathrm{Ca}\right)$. The trap is loaded from an atomic beam which is decelerated in a Zeeman slower and subsequently deflected over an angle of 30° by optical molasses. The isotope selectivity of the Zeeman slower and the deflection stage is investigated experimentally and compared with Monte Carlo simulations.

Figure 1

A schematic overview of the experimental setup.

Figure 2

The fluorescence of calcium isotopes in an atomic beam after a single excitation step.

Figure 3

Fluorescence in the trap loaded from oven 2. The background signal is caused by ${}^{40}\mathrm{Ca}$ passing through the trap with its Maxwell-Boltzmann velocity distribution and excited by the horizontal trapping laser beams.

Figure 4

Fluorescence in the trap loaded from a slowed but not deflected atom beam. This spectrum was taken before the deflection stage was installed (see Fig. 1).

Figure 5

Fluorescence in the trap loaded from a slowed and deflected beam.

Figure 6

Fluorescence intensity of ${}^{43}\mathrm{Ca}$ and background level intensity for two different oven temperatures. The ${}^{43}\mathrm{Ca}$ peak intensity increases by a factor of 6.6, while the fluorescence background level remains almost constant.

Figure 7

A calculation of the final longitudinal velocity distribution (1000 atoms each) of the isotopes ${}^{40}\mathrm{Ca}$, ${}^{41}\mathrm{Ca}$, and ${}^{42}\mathrm{Ca}$ traveling through the Zeeman slower. The laser detuning is set for ${}^{41}\mathrm{Ca}$. An example of a Monte Carlo sampling of the initial velocity distribution upon entering the Zeeman slower is shown in the top panel.

Figure 8

A simulation of the large-angle atomic beam deflection for the different isotopes. Shown is the deflection angle as a function of the initial velocity for three different isotopes: ${}^{40}\mathrm{Ca}$, ${}^{41}\mathrm{Ca}$, and ${}^{42}\mathrm{Ca}$. The inset shows the geometry of the atomic beam and the deflection laser beams. The laser is $40\mathrm{MHz}$ red detuned with respect to the ${}^{41}\mathrm{Ca}$ resonance frequency. Further details are given in the text.

Figure 9

Fluorescence of individual atoms detected in the MOT. The dotted lines indicate the fluorescence level for one, two, and three atoms in the trap. The integration time of the photon detector is $4\mathrm{ms}$.