Strong coupling of single cesium atoms with a high-finesse optical micro-cavity (the finesse of our Fabry-Perot-type micro-cavity is F = 3.3 x 105 and the cavity length is lc = 86 μm) has been realized for the both cases of TEM00 and TEM10 cavity modes in our experiments. The typical parameters are (g00, κ, Υ) = 2π x (23.9, 2.6, 2.6) MHz and (g10, κ, Υ) = 2π x (20.5, 2.6, 2.6) MHz for these two cases, respectively. Obviously our system reaches the strong coupling regime. The first application is to adopt strong coupling of free-fall individual atoms with the TEM00 cavity mode for determining the effective temperature of laser-cooled atoms prepared in a magneto-optical trap located just above the micro-cavity. The second application is to employ strong coupling of free-fall individual atoms with the tilted TEM10 cavity mode, in stead of TEM00 mode, for more precisely tracking the trajectories of atoms passing through the cavity mode.
Strong coupling of single cesium atoms with a high-finesse optical micro-cavity (the finesse of our Fabry-Perot-type micro-cavity is F = 3.3 x 105 and the cavity length is lc = 86 μm) has been realized for the both cases of TEM00 and TEM10 cavity modes in our experiments. The typical parameters are (g00, κ, Υ) = 2π x (23.9, 2.6, 2.6) MHz and (g10, κ, Υ) = 2π x (20.5, 2.6, 2.6) MHz for these two cases, respectively. Obviously our system reaches the strong coupling regime. The first application is to adopt strong coupling of free-fall individual atoms with the TEM00 cavity mode for determining the effective temperature of laser-cooled atoms prepared in a magneto-optical trap located just above the micro-cavity. The second application is to employ strong coupling of free-fall individual atoms with the tilted TEM10 cavity mode, in stead of TEM00 mode, for more precisely tracking the trajectories of atoms passing through the cavity mode.
Cavity quantum electrodynamics (cavity QED) describes electromagnetic fields in a confined space and the radiative properties of atoms in such fields. The simplest example of such system is a single atom interacting with one mode of a high-finesse resonator. Besides observation and exploration of fundamental quantum mechanical effects, this system bears a high potential for applications quantum information science such as, e.g., quantum logic gates, quantum communication and quantum teleportation. In this thesis I present an experiment on the deterministic coupling of a single neutral atom to the mode of a high-finesse optical resonator. In Chapter 1 I describe our basic techniques for trapping and observing single cesium atoms. As a source of single atoms we use a high-gradient magneto-optical trap, which captures the atoms from background gas in a vacuum chamber and cools them down to millikelvin temperatures. The atoms are then transferred without loss into a standing-wave dipole trap, which provides a conservative potential required for experiments on atomic coherence such as quantum information processing and metrology on trapped atoms. Moreover, shifting the standing-wave pattern allows us to deterministically transport the atoms (Chapter 2). In combination with non-destructive fluorescence imaging of individual trapped atoms, this enables us to control their position with submicrometer precision over several millimeters along the dipole trap. The cavity QED system can distinctly display quantum behaviour in the so-called strong coupling regime, i.e., when the coherent atom-cavity coupling rate dominates dissipation in the system. This sets the main requirements on the resonator's properties: small mode volume and high finesse. Chapter 3 is devoted to the manufacturing, assembling, and testing of an ultra-high finesse optical Fabry-Perot resonator, stabilized to the atomic transition. In Chapter 4 I present the transportation of single atoms into the cavity and their coupling to the cavity mode. The strong coupling manifests itself in a strong reduction of the cavity transmission probed by a weak external laser. The atoms remain trapped and coupled to the cavity mode for several seconds until we move them out of the cavity for final analysis of their number and position.
Cavity quantum electrodynamic system with strongly coupled single atoms provides a good platform for studying quantum information processing, quantum simulation, quantum network, and distributed quantum computing. Cooling and trapping single atoms is a crucial technique in the quantum technology. At present, in a high-finesse cavity with finite space, cooling and trapping single atoms is a big challenge, even though it is a mature technique for free space. Great efforts have been made to cool and trap single atoms inside a cavity, and for a trapped atom its lifetime has reached as long as tens of seconds. Developing a more flexible method of cooling and trapping single atoms in a cavity is still essential for a strongly coupled cavity quantum electrodynamic system. In this work, we demonstrate experimentally that a single cesium atom in a cavity can be trapped by utilizing a single optical tweezer settled in cavity mode, and its lifetime is (2.60 ± 0.18) s. The experiment is carried out in a Fabry-Perot cavity, which is assembled by two concave mirrors each with a curvature radius of 100 mm, and cavity length of 335 μm. The concave surfaces are highly reflective, and the cavity has a finesse of 6.1 × 104. The 1080 nm optical tweezer with a waist of 2 μm is formed by an achromatic lens group with a numerical aperture of 0.4. At first, the precooled atomic assemble released from the magneto-optical trap (MOT) is transferred into cavity mode by an optical dipole trap with a waist of 36 μm. Then, one of the successfully transferred atoms is captured by the optical tweezer with the aid of cavity cooling mechanism. A blue detuned cavity locking laser is used as a standing-wave optical trap along the cavity axis. The signal of successfully trapped one atom is obtained by recording transmission of the cavity that will decrease owing to the strong coupling induced vacuum Rabi splitting. Finally, we demonstrate the precise manipulation of the atom-cavity coupling strength, which is achieved by scanning the position of the trapped atom step by step by using a high-precision translation stage. The system realized in this work can be used to study the dynamics of single atom-photon interactions with adjustable coupling strength. In addition, the mechanism adopted in this work is compatible with constructing tweezer arrays inside cavity mode, and thus possesses more flexibility and great potentials in cavity-based quantum entanglement and quantum simulation.
We experimentally demonstrate real-time detection of individual cesium atoms by using a high-finesse optical micro-cavity in a strong coupling regime. A cloud of cesium atoms is trapped in a magneto-optical trap positioned at 5 mm above the micro-cavity center. The atoms fall down freely in gravitation after shutting off the magneto-optical trap and pass through the cavity. The cavity transmission is strongly affected by the atoms in the cavity, which enables the micro-cavity to sense the atoms individually. We detect the single atom transits either in the resonance or various detunings. The single atom vacuum-Rabi splitting is directly measured to be Ω = 2π × 23.9 MHz. The average duration of atom-cavity coupling of about 110 μs is obtained according to the probability distribution of the atom transits.
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 TEM10 mode, instead of the usual TEM00 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 TEM10 mode are detected by single-photon counting modules and are well fitted. Thanks to the tilted cavity transverse TEM10 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, $186\ifmmode\pm\else\textpm\fi{}19 \ensuremath{\mu}\text{K}$.
We have used a fiber Fabry-Perot cavity on an atom chip to obtain strong, extremely stable atom-cavity coupling for single atoms and Bose-Einstein condensates trapped inside the cavity. The coherent atom-cavity coupling parameter, g0/2pi ~ 209 MHz, is larger than both cavity decay, kappa/2pi ~ 53 MHz and spontaneous emission gamma/2pi ~ 3 MHz. Due to the small mode volume, these values, well inside the strong coupling regime of cavity QED, are realized with a cavity finesse F ~ 36000, which is a moderate value compared to usual strong-coupling cavity QED experiments. The cavity also achieves a very high cooperativity parameter, C=g02/2kappagamma ~ 130.The use of trapped Bose-Einstein condensates (BECs) is a fundamentally new situation for cavity QED, which should enable a new class of experiments, where atoms that share a well-defined internal and external quantum state collectively interact with a quantized mode of the cavity. Besides, as the spatial extension of the BEC assumes the fundamental limit that can be attained for an atom cloud - much smaller than an optical wavelength in our case - an extremely strong, stable and uniform coupling to the cavity mode is achieved. This makes the system interesting for applications such as quantum memories. For single atoms, our combination of high resonator cooperativity with extreme positioning precision enables qubit detection with near-unit efficiency. This realizes a long-awaited milestone for quantum information processing on atom chips.
While for the most part quantum statistical processes in quantum optics are investigated in a weak coupling regime, it has recently become possible to realize experimentally optical systems for which the internal coupling coefficient g is comparable to the external dissipative rates. Within this context the subject of our investigation is the quantum dynamical processes for a collection of N two-state atoms strongly coupled to a single mode of a high finesse optical cavity, Our particular experiment consists of a small collection of Cesium atoms (6S1/2, F = 4 → 6P3/2, F = 5 transition at 852nm) interacting with the TEM00 mode of a spherical mirror cavity. The critical technical advance for this work is the attainment of extremely low loss mirrors for high finesse (103 – 106) and hence long photon lifetime even in a small cavity.[1]