State-Insensitive Cooling and Trapping of Single Atoms in an Optical Cavity

Single cesium atoms are cooled and trapped inside a small optical cavity by way of a novel far-off-resonance dipole-force trap, with observed lifetimes of $2–3\mathrm{s}$. Trapped atoms are observed continuously via transmission of a strongly coupled probe beam, with individual events lasting $\simeq 1\mathrm{s}$. The loss of successive atoms from the trap $N\ge 3\to 2\to 1\to 0$ is thereby monitored in real time. Trapping, cooling, and interactions with strong coupling are enabled by the trap potential, for which the center-of-mass motion is only weakly dependent on the atom’s internal state.

Figure 1

ac-Stark shifts $({\widehat{\delta }}_{6S_{1/2}},{\widehat{\delta }}_{6P_{3/2}})$ for the $(6S_{1/2},6P_{3/2})$ levels in Cs for a linearly polarized FORT. The inset shows $({\widehat{\delta }}_{6S_{1/2}},{\widehat{\delta }}_{6P_{3/2},F^{\prime }=4})$ as functions of wavelength ${\lambda }_F$. The full plot gives ${\widehat{\delta }}_{6P_{3/2}}$ versus $m_{F^{\prime }}$ for each of the levels $6P_{3/2}$, $F^{\prime }=2,3,4,5$ for ${\lambda }_F=935.6\mathrm{n}\mathrm{m}$. In each case, the normalization is $\widehat{\delta }=\delta /[{\delta }_{6S_{1/2}}({\lambda }_F=935.6\mathrm{n}\mathrm{m})]$.

Figure 2

Schematic of experiment for trapping single atoms in an optical cavity in a regime of strong coupling. Relevant cavity parameters are length $l=43.0\mathrm{\mu }\mathrm{m}$, waist $w_0=23.9\mathrm{\mu }\mathrm{m}$, and finesse $\mathcal{F}=4.2\times {10}^5$ at $852\mathrm{n}\mathrm{m}$. The inset illustrates transverse beams used for cooling and repumping.

Figure 3

(a) Detection probability $P$ as a function of trapping time $t_T$. The upper data set is for mean intracavity atom number $\overline{N}\approx 0.30$, while the lower set is for $\overline{N}\approx 0.019$ atoms. Exponential fits (solid lines) yield lifetimes ${\tau }_{\mathrm{u}\mathrm{p}\mathrm{p}\mathrm{e}\mathrm{r}}=(2.4\pm 0.2)\mathrm{s}$ and ${\tau }_{\mathrm{l}\mathrm{o}\mathrm{w}\mathrm{e}\mathrm{r}}=(2.0\pm 0.3)\mathrm{s}$. (b) The fractional population $f_4(t_D)$ in $F=4$ following depletion of this level at $t_D=0$. An exponential fit (solid line) gives ${\tau }_R=(0.11\pm 0.02)\mathrm{s}$.

Figure 4

Two traces of the continuous observation of trapped atoms inside a cavity in a regime of strong coupling. After an initial sharp reduction around $t=0$ as atoms are cooled into the cavity mode, the intracavity field strength $\overline{m}$ increases in a discontinuous fashion as trapped atoms escape from the cavity mode one by one. rf detection bandwidth $=1\mathrm{k}\mathrm{H}\mathrm{z}$, ${\Delta }_C^{\prime }=0={\Delta }_p^{\prime }$, and ${\Delta }_3/2\pi =25\mathrm{M}\mathrm{H}\mathrm{z}$.