In this thesis a single atom is trapped in the mode of a high-finesse cavity and used to generate single photons in a controlled way. Starting from a magneto-optical trap, rubidium atoms are loaded into an optical dipole-force trap and transported to the cavity. On arrival the atoms are trapped in another trap with a standing wave geometry and excited by a pump laser incident perpendicular to the cavity axis. With the help of cavity cooling forces, a single atom could then be selected and trapped for up to a minute. A sequence of laser pulses is applied to induce the emission of a stream of single photons from the atom. Up to 300000 photons could be generated from the same atom in this way. The single-photon character of the source is verified within a few seconds after which the photons can be distributed to an independent user while monitoring the presence of the atom.
In this thesis a single atom is trapped in the mode of a high-finesse cavity and used to generate single photons in a controlled way. Starting from a magneto-optical trap, rubidium atoms are loaded into an optical dipole-force trap and transported to the cavity. On arrival the atoms are trapped in another trap with a standing wave geometry and excited by a pump laser incident perpendicular to the cavity axis. With the help of cavity cooling forces, a single atom could then be selected and trapped for up to a minute. A sequence of laser pulses is applied to induce the emission of a stream of single photons from the atom. Up to 300000 photons could be generated from the same atom in this way. The single-photon character of the source is verified within a few seconds after which the photons can be distributed to an independent user while monitoring the presence of the atom.
A single rubidium atom trapped within a high-finesse optical cavity is an efficient source of single photons. We theoretically and experimentally study single-photon generation using a vacuum stimulated Raman adiabatic passage. We experimentally achieve photon generation efficiencies of up to 34 and 56 on the D1 and D2 line, respectively. Output coupling with 89 results in record-high efficiencies for single photons in one spatiotemporally well-defined propagating mode. We demonstrate that the observed generation efficiencies are constant in a wide range of applied pump laser powers and virtual level detunings. This allows for independent control over the frequency and wave packet envelope of the photons without loss in efficiency. In combination with the long trapping time of the atom in the cavity, our system constitutes a significant advancement toward an on-demand, highly efficient single-photon source for quantum information processing tasks.
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.
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.
The experiments discussed in this thesis focus on the interaction of a single trapped atom with the single mode of a high-finesse optical cavity, in the regime of strong coupling. Chapter 1 gives a brief introduction, after which Chapter 2 describes our recent measurements of the transmission spectrum of the atom-cavity system. The spectrum exhibits a clearly resolved vacuum-Rabi splitting, in good quantitative agreement with theoretical predictions. A new Raman scheme for cooling atomic motion along the cavity axis enables a complete spectrum to be recorded for an individual atom trapped within the cavity mode, in contrast to all previous measurements of this type that have required averaging over 10^3-10^5 atoms. Chapter 3 discusses our observations of photon blockade for the transmitted light in the presence of one trapped atom. Excitation of the atom-cavity system by a first photon blocks the transmission of a second one, thereby converting an incident Poissonian stream of photons into a sub-Poissonian, anti-bunched stream, as confirmed by measurements of the photon statistics of the transmitted field. The intensity correlations of the cavity transmission also reveal the energy distribution for oscillatory motion of the trapped atom. Chapter 4 details a set of simple but necessary measurements of relevant experimental parameters such as cavity geometry, linewidth, mirror properties, birefringence, and detection efficiency. The thesis concludes with Appendix A, describing the efficient laser setup we use for our magneto-optical traps.
Summary form only given. The strong coupling between an atom and the light field in an optical microresonator causes a single atom to alter the transmission of the cavity significantly, allowing its continuous observation. At the same time, the strong coupling leads to novel optical forces acting on the atom. It was predicted that it should be possible to trap an atom with single intracavity photons. Using an atomic fountain, we inject single ultracold neutral atoms in the standing-wave light field of a high-finesse optical cavity. When an atom is detected in the cavity, the laser light pumping the cavity is suddenly switched to a higher value. This increases the depth of the optical dipole potential and traps the atom in the cavity field.
Cooling is indispensable for trapping and observing single free atoms.In atomic physics, this can be achieved efficiently by laser cooling.Conventional methods to laser cool atoms are based on repeated optical pumping cycles followed by spontaneous emission of a photon from the atom.Such pumping schemes can only be applied to certain atomic species, which have a closed optical transition.Drawbacks caused by photons spontaneously emitted from the atom can be avoided in the strongly coupled atom-cavity system in which energy and entropy can be removed by photons lost from the cavity.This thesis reports on the first observation of this cooling mechanism which does not rely on spontaneous emission.In the experiment, a single atom is captured in an intracavity dipole trap.Illuminating the system with a weak, slightly blue-detuned light beam extends the storage time of the atom in the trap.The observed cooling force is at least five times larger than the force achieved by free-space cooling methods at comparable excitation of a two-level atom.Utilising cavity cooling, single atoms are prepared strongly-coupled to the mode of a high-finesse cavity.This allows to observe two well-resolved normal-mode peaks in both the cavity transmission as well as in the trap lifetime.The experiment is in agreement with a Monte Carlo simulation, demonstrating the localisation of the atom to within a tenth of a wavelength.The ability to individually excite the normal modes opens new possibilities to use this system for applications in quantum information science, including the realisation of quantum-logic gates.In the future cavity cooling might be applied to systems which cannot be cooled by conventional methods as for instance molecules or an atom carrying a quantum bit.