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.
A new method to track the motion of a single particle in the field of a high-finesse optical resonator is analyzed. It exploits sets of near-degenerate higher-order Gaussian cavity modes, whose symmetry is broken by the position dependent phase shifts induced by the particle. Observation of the spatial intensity distribution outside the cavity allows direct determination of the particle's position. This is demonstrated by numerically generating a realistic atomic trajectory using a semiclassical simulation and comparing it to the reconstructed path. The path reconstruction itself requires no knowledge about the forces on the particle. Experimental realization strategies are discussed.
A coupled quantum system composed of cavity field and atoms is one of the main research contents of cavity quantum electrodynamics. It can be used to realize single atom manipulation and measurement, and has important significance for studying the interaction between light and the atom, preparing quantum states and quantum entanglement. Current research work mainly focuses on two aspects. One is to achieve the atom trapping via the feedback control of the trapping laser intensity. The other is to measure the single atomic motion in a Fabry-Perot cavity by using Hermite-Gaussian transverse modes. The detection of the atomic trajectories has been realized via the observation of transmission spectra of the strong coupling system composed of cold atoms and Hermite-Gaussian transverse modes in a Fabry-Perot cavity. In order to observe the atomic motion trajectories in the cavity, we theoretically study the transmission spectrum of a strong coupling system composed of cold atoms and Laguerre-Gaussian transverse modes in a Fabry-Perot cavity in this paper. We calculate the relationship between the coupling coefficient and the mode number of Laguerre-Gaussian transverse modes. The result shows that with the increase of Laguerre-Gaussian transverse mode number, the maximum coupling coefficient between the atoms and cavity fields is almost unchanged, so the contrast of the detected spectrum is nearly independent of the mode number. Analysis shows that Laguerre-Gaussian transverse mode provides more abundant information about atomic motion trajectory than Hermite-Gaussian transverse mode. The field distribution of Laguerre-Gaussian transverse mode is ring-shaped. Owing to the ring shape, the atoms dropped at different positions experience different electric field intensities, and the detected transmission spectra are changed. Therefore, we can implement the high precision distinguishment of the atomic trajectories by observing the features of the transmission spectra such as the number of the transmission peaks and their positions. Furthermore, a small deviation of the atomic motion trajectories, on the edges of the rings of the electric field, may induce great change in transmission spectrum, and then we can very accurately detect the atomic motion around these positions.
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, $186\ifmmode\pm\else\textpm\fi{}19 \ensuremath{\mu}\text{K}$.
Summary form only given. The strong atom-photon coupling generated inside high-finesse optical micro cavity lets us detect a single atom trajectory in real time. Such a strong coupling is a candidate for trapping a single atom with a single photon. Dynamics of trapped atoms can be observed in situ and in real time by detecting intensity change on the transmission of a blue-shifted laser beam. We cooled down and trapped rubidium atoms by using conventional cell magneto optical trap (MOT) and launched them into the micro optical cavity which locates 35 mm above the MOT. By using this signal as trigger and changing the laser frequency, it is, in principle, possible to trap the atom in the cavity.