We have experimentally demonstrated the strong coupling between single atoms and the higher-order Hermite-Gaussian transverse modes in a high-finesse optical microcavity. Compared to the usual low-order symmetric transverse modes, multiple lobes and the asymmetric spatial pattern of the titled modes provide more information about the motion of single atoms in the cavity. The motional information can be extracted from the measured transmission spectra, which includes the velocities and the positions of the atoms in vertical and off-axis directions. The scheme has great potential in time-resolved atom-cavity microscopy and in tracking the three-dimensional single atom trajectory in real time.
We demonstrate the trajectory measurement of the single neutral atoms deterministically using a high-finesse optical microcavity. The single atom strongly couples to the high-order transverse vacuum TEM
10 mode, instead of the usual TEM
00 mode, and the parameters of the system are $({g}_{10},\ensuremath{\kappa},\ensuremath{\gamma})=2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}(20.5,2.6,2.6) \text{MHz}$. The atoms simply fall down freely from the magneto-optical trap into the cavity modes, and the trajectories of the single atoms are linear. The transmission spectra of atoms passing through the TEM
10 mode are detected by single-photon counting modules and are well fitted. Thanks to the tilted cavity transverse TEM
10 mode, which is inclined to the vertical direction
${45}^{\ifmmode^\circ\else\textdegree\fi{}}$, it helps us to eliminate the degenerate trajectory of the single atom falling through the cavity and to obtain a unique atom trajectory. An atom position with a high precision of $0.1 \ensuremath{\mu}\text{m}$ in the off-axis direction (axis
y) is obtained, and a spatial resolution of $5.6 \ensuremath{\mu}\text{m}$ is achieved in a time interval of $10 \ensuremath{\mu}\text{s}$ along the vertical direction (axis
x). The average velocity of the atoms is also measured from the atom transits, which determines independently the temperature of the atoms in a magneto-optical trap, $186\ifmmode\pm\else\textpm\fi{}19 \ensuremath{\mu}\text{K}$.