A neutral atom interacting with a single mode of a high finesse cavity provides an opportunity to study uncharted quantum mechanical systems and to explore the field of quantum computing and networking. Ranging from being a deterministic single photon source to a coherent storage unit for quantum information, a strong coupling cavity QED system has proven to be a powerful tool. In this thesis, single atoms are deterministically delivered over long distances and probed in an optical cavity. Once in the cavity, a single atom is stored and continuously observed for over 15 seconds. Progress towards using atoms in the cavity to produce entangled photon pairs is presented. Dual 1D optical lattices are implemented to create a foundation for advancements in two qubit quantum operations and entanglements.
A neutral atom interacting with a single mode of a high finesse cavity provides an opportunity to study uncharted quantum mechanical systems and to explore the field of quantum computing and networking. Ranging from being a deterministic single photon source to a coherent storage unit for quantum information, a strong coupling cavity QED system has proven to be a powerful tool. In this thesis, single atoms are deterministically delivered over long distances and probed in an optical cavity. Once in the cavity, a single atom is stored and continuously observed for over 15 seconds. Progress towards using atoms in the cavity to produce entangled photon pairs is presented. Dual 1D optical lattices are implemented to create a foundation for advancements in two qubit quantum operations and entanglements.
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 electrodynamics (QED), the system of a single atom interacting with a single mode of a high finesse optical resonator, has tremendous potential for use in quantum logic, quantum information processing, and in enabling observation of quantum mechanical effects in the laboratory. The work of this thesis demonstrates a number of steps toward realizing these goals, by employing an experimental system with the strongest atom-field coupling achieved to date in optical cavity QED. The effects of strong coupling in cavity QED are studied for single cold atoms measured one at a time, in real time. The passage of single atoms through the cavity is employed to map out the frequency response of the system, and to demonstrate that quantum rather than semiclassical theory provides the correct theoretical model. The mechanical effects of strong coupling on single atoms are explored, these experiments demonstrating the first trapping of single atoms with single photons. Additionally, strong coupling enables high signal-to-noise ratio for monitoring atomic position at single photon field strengths; this capability is employed to investigate the motion of atoms trapped within the cavity. The transmitted cavity field is used to reconstruct the trajectories of single atoms, thereby realizing a new form of microscopy - the Atom-Cavity Microscope. Technical developments necessary to create the cavities used in this experiment are detailed. Ideas for future extensions to the experiment are proposed; a zero light-shift dipole force trap, and measurement of photon statistics of a single strongly coupled atom (which realizes a photon blockade device) are discussed.
Ultracold neutral atoms confined in optical dipole traps have important applications in quantum computation and information processing, quantum simulators of interacting-many-body systems and atomic frequency metrology. While optical dipole traps are powerful tools for cold atom experiments, the energy level structures of the trapped atoms are shifted by the trapping field, and it is important to characterize these shifts in order to accurately manipulate and control the quantum state of the system.\n\nIn order to measure the light shifts, we have designed a system that allows us to reliably trap individual 87Rb atoms. A non-destructive detection technique is employed so that the trapped atoms can be continuously observed for over 100 seconds. Single atom spectroscopy, trap frequency measurements, and temperature measurements are performed on single atoms in a single focus trap and small number of atoms in a 1D optical lattice in order to characterize the trapping environment, the perturbed energy level structures, and the probe-induced heating.\n\nIn the second part of the thesis, we demonstrate deterministic delivery of an array of individual atoms to an optical cavity and selective addressability of individual atoms in a 1D optical conveyor, which serves as a potential candidate for scalable quantum information processing. The experiment is extended to a dual lattice system coupled to a single cavity with the capability of independent lattice control and addressability. The mutual interactions of atoms in different lattices mediated by a common cavity field are demonstrated. A semi-classical model in the many-atom regime based on the Jaynes-Cummings model is developed to describe the system that is in good qualitative agreement with the data. This work provides a foundation for developing multi-qubit quantum information experiments with a dual lattice cavity system.
Neutral atoms are ideal objects for the deterministic processing of quantum information. Entanglement operations have been performed by photon exchange or controlled collisions. Atom-photon interfaces were realized with single atoms in free space or strongly coupled to an optical cavity. A long standing challenge with neutral atoms, however, is to overcome the limited observation time. Without exception, quantum effects appeared only after ensemble averaging. Here we report on a single-photon source with one-and-only-one atom quasi permanently coupled to a high-finesse cavity. Quasi permanent refers to our ability to keep the atom long enough to, first, quantify the photon-emission statistics and, second, guarantee the subsequent performance as a single-photon server delivering up to 300,000 photons for up to 30 seconds. This is achieved by a unique combination of single-photon generation and atom cooling. Our scheme brings truly deterministic protocols of quantum information science with light and matter within reach.
As quantum computers advance toward larger, more powerful systems, scaling beyond a single quantum processing unit (QPU) will require the development of fast, high-fidelity interconnections between QPUs. One of the most promising strategies for achieving this is coupling qubits to optical cavities. Strong atom-cavity interactions enable the generation of atom-photon entanglement at rates orders of magnitude faster than alternative approaches, offering a critical advantage for scalable architectures. This thesis investigates the use of nanophotonic and microscale cavities to achieve exceptional atom-photon coupling while maintaining compatibility with state-of-the-art neutral atom QPUs. The experiments presented in this thesis demonstrate coherent transport between a free-space atom array and an optical cavity, coherent Rydberg excitations and interactions in the presence of the cavity interface, fast high-fidelity readout and cavity-mediated operations, and novel fabrication techniques for improved microcavities that further enhance system performance. Together, these advances outline a pathway toward utility-scale quantum computing.