In this thesis, a model system of quantum optics is experimentally studied - a single atom coupled to a high-finesse optical cavity. Upon excitation with laser pulses, the atom-cavity system undergoes vacuum Rabi oscillations between the atom and the cavity field. This is accompanied by the controlled emission of single photons. The optical resonator also enables efficient state detection of single neutral atoms. We introduce a method based on cavity-enhanced fluorescence and achieve a fidelity of 99.4 % for the detection of the atomic hyperfine state within 85 µs. Further, this thesis presents experiments on electromagnetically induced transparency with a single atom and on phase shaping of single photon wave packets. The atom-cavity system has promising applications in quantum information science.
In this thesis, a model system of quantum optics is experimentally studied - a single atom coupled to a high-finesse optical cavity. Upon excitation with laser pulses, the atom-cavity system undergoes vacuum Rabi oscillations between the atom and the cavity field. This is accompanied by the controlled emission of single photons. The optical resonator also enables efficient state detection of single neutral atoms. We introduce a method based on cavity-enhanced fluorescence and achieve a fidelity of 99.4 % for the detection of the atomic hyperfine state within 85 µs. Further, this thesis presents experiments on electromagnetically induced transparency with a single atom and on phase shaping of single photon wave packets. The atom-cavity system has promising applications in quantum information science.
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.
In recent years, remarkable advances in the science of laser cooling and trapping of atomic samples have lead to breakthroughs in quantum optics and, in particular, in cavity quantum electrodynamics (QED). The ability to optically trap an atom within the mode of a ultra-high finesse cavity of small mode volume for experimentally significant periods of time now allows for the continuous observation of fundamental quantum optical effects. This dissertation will focus on experiments conducted to fully characterize and exert quantum control over a strongly-coupled atom-cavity system consisting of single cesium atoms isolated by a dipole trapping in the mode of a Fabry-Perot optical resonator. In particular, we describe techniques developed and implemented for exerting coherent control over the internal and quantum motional state of these atoms using stimulated Raman processes. We also focus on the applications of this system to quantum networking and quantum information science, particularly within the context of coherently transferring quantum states from atom to quantum optical fields and back. Finally, we describe a series of measurements carried out to explore the characteristic dynamics of the Jaynes-Cummings Hamiltonian which governs the system. This includes spectroscopic measurement of the signature vacuum Rabi splitting for strongly-coupled cavity QED as well as evidence in the time domain for coherent Rabi nutation of excitation between atom and field on resonance.
A system comprised of a small number of neutral atoms coupled to the mode of a high finesse optical resonator is a model system to study light-matter interaction at the quantum level and to explore fundamental effects like the influence of the measurement process on the atomic state. Promising proposals to generate entangled states in such systems are based on the simultaneous coupling of two atoms to one resonator mode. In chapter 1 of this thesis I shortly summarise the experimental tools to capture, trap, and transport single atoms using a magneto-optical trap and an optical conveyor belt. I discuss theoretical foundations to describe our system and present numerical simulations, the results of which enter the analysis of our experimental data. The average atom-cavity coupling strength is deduced from the measured cavity transmission and compared to a model taking atomic motion into account. The dynamics of the hyperfine spin state of one and two coupled atoms is the focus of chapter 2. I describe a nondestructive cavity-based state detection method, quantify the state detection fidelity, and identify optimum experimental parameters. This method is then used to record random telegraph signals, exhibiting quantum jumps on a timescale of milliseconds. Telegraph signals for two atoms are analysed employing Bayesian statistics, yielding additional information on the evolution of the hyperfine states. A good localisation of the atom is necessary to achieve stable coupling to the cavity mode. In chapter 3, I discuss two different aspects of how the motion of the atom can be controlled. Firstly an intracavity dipole trap is characterised and it is shown that it results in improved confinement of the atom. Secondly I examine the dependence of cavity-cooling forces on our experimental parameters and compare two different cooling regimes.
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.
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.
Neutral atom arrays have rapidly emerged as a leading platform for quantum computing, boasting scalable, configurable arrays of single atoms trapped in optical tweezers, fast, high-fidelity entangling gates through Rydberg interactions, and programmable, parallelized control of qubit operations. Coupling an atom array to an optical cavity opens a new frontier. Leveraging enhanced light-atom interactions in cavity quantum electrodynamics, cavity- coupled atom arrays acquire capabilities that can further expand the neutral atom toolbox, including cavity-enhanced atom readouts, atom-photon entanglement, and photon-mediated interactions between distant atoms. This thesis presents a quantum hardware platform that integrates an array of neutral atoms with a high-finesse optical cavity. After describing the design and development of the experimental apparatus, I demonstrate high-fidelity atom state readout through the cavity, achieving improved speed and atom survival compared to conventional free-space imaging methods. I then introduce a new technique for selectively controlling atom-cavity coupling on arbitrary subsets of the array, using local AC Stark shifts on the excited states of the atoms. Building on these tools, I demonstrate fast, non-destructive cavity-based readout of atom arrays, a crucial bottleneck of atom array platforms. I also showcase real-time measurement and feedback capabilities with a demonstration of classical error correction, using a register of atomic bits. Finally, I describe progress toward implementing single- and two-qubit gates within the cavity-coupled system. By combining coherent control, tunable interactions, and high-fidelity, non-destructive readout integrated and real-time feedback, the cavity-coupled Rydberg atom array offers a promising path toward fault-tolerant quantum computing.