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.
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.
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.
Neutral atom arrays have emerged as one of the leading platforms for quantum computation and simulation. Integrating these arrays with photonic interfaces, such as optical cavities, enables high-speed qubit readout, efficient atom-photon entanglement, and novel quantum simulation capabilities through long-range interactions. However, achieving scalable and efficient integration of atom arrays with photonic structures remains a significant challenge. In this work, we present an atom-array cavity-array platform that integrates cesium atom arrays with a photonic chip containing over 100 nanophotonic cavities. This platform inherently supports multiplexing by allowing simultaneous interactions between multiple atoms and multiple cavities, a crucial capability for scaling up quantum information processing and networking. To enable this integration, we develop three key techniques: (1) a backgroundfree imaging scheme utilizing excited-state transitions in cesium with fidelity exceeding 99%, (2) a photonic chip design optimized for efficient atom loading, and (3) a free-space coupling scheme achieving over 65% waveguide-to-fiber coupling efficiency. We demonstrate collisional blockade-limited loading of atom arrays near the photonic chip, parallel transport of atoms to multiple cavities, a key capability that enables the multiplexing required in quantum networks and distributed quantum computing. Finally, we show an array of resonant telecom cavities, and multiple theoretical architectures to make use of these to distribute entanglement across hundreds of kilometers. These results address critical challenges in atom-photon integration and pave the way for scalable quantum information processing.
Realizing an efficient quantum optical interface for multi-qubit systems would enable their quantum network integration and the scaling-up of the qubit number via distributed quantum computing. This thesis presents the building blocks for integrating a quantum processor based on a Rydberg atom array with a nanophotonic cavity as an optical interface. In our approach, the integration would be achieved by coherently transporting tweezer-trapped atoms between the cavity near-field and free space. To that end, we first characterize the strong coupling between single photons and atoms enabled by the nanophotonic device. Two 87Rb atoms are trapped in optical tweezers and brought to the cavity near-field, while the cavity is probed in reflection. We observe Purcell enhancement and cavity-mediated interactions between the atoms, corresponding to a single atom cooperativity of C = 70 in the mode center. The qubits are encoded in atomic hyperfine ground states, which have good coherence properties even when the atoms are trapped in the cavity near-field. We create an atomic Bell state by pairing up the coherent manipulation of atomic qubits with a quantum nondemolition measurement, implemented via a single photon reflection from the cavity. Crucial to the integration, we show that single atom coherence and two-atom entanglement can be preserved as the atoms are moved away from the cavity. The nanophotonic dielectric surface can host charges which affect highly polarizable Rydberg states, and this influence is studied by measuring the n = 70 Rydberg state coherence at different distances from the cavity. Our measurements suggest that a Rydberg array may be placed ∼ 200 μm away from a nanophotonic device while retaining high quantum gate fidelities. Our methods can be applied to other atomic species and device geometries, paving the path to quantum networks of Rydberg array processors.
Scalable quantum computers and quantum networks require the combination of quantum processing nodes with efficient light-matter interfaces to distribute quantum information in local or long-distance quantum networks. Neutral-atom arrays have both been coupled to Rydberg states to enable high-fidelity quantum gates in universal processing architectures, and to optical cavities to realize interfaces to photons. However, combining these two capabilities and coupling atom arrays to highly excited Rydberg states in the mode of an optical cavity has been an outstanding challenge. Here we present a novel cavity-coupled Rydberg array that achieves this long-standing goal. We prepare, detect, and control individual atoms in a scalable optical tweezer array, couple them strongly to the optical mode of a high-finesse optical cavity and excite them in a controlled way to Rydberg states. We show that high-cooperativity coupling to an optical cavity -- demonstrated via the dispersive shift of the resonance of the cavity in presence of the atoms -- and strong Rydberg interactions -- demonstrated via the collective enhancement of Rydberg coupling in the atomic array -- can be achieved in our setup at the same spatial location. Our presented experimental platform opens the path to several new directions, including the realization of quantum network nodes, quantum simulation of long-range interacting, open quantum systems and photonic-state engineering leveraging high-fidelity Rydberg control.
Platforms consisting of neutral atoms individually trapped in arrays of optical tweezers have achieved important milestones in quantum simulation and quantum computation. With access to programmable Rydberg interactions, individual qubit control, long coherence times, and naturally identical qubit transitions, neutral atoms are a promising building-block for the use in future quantum machines. However, they face the same challenge as other quantum platforms in scaling the number of qubits needed to perform algorithms with a provable advantage over classical computers. An avenue toward scaling systems of neutral atoms may be to use a quantum network that connects individual systems to construct a distributed computing architecture. Key to this approach is for the atoms to have access to an efficient optical interface, where the quantum information can be mapped to a single photon and sent across a quantum network. This thesis explores using a nanophotonic crystal cavity to act as this interface. With our device, we have demonstrated high-cooperativity coupling of two atoms to the photonic mode, generated entanglement at the device using a projective measurement, and coherently transported an entangled pair of atoms away from the device. Furthermore, we have taken the first steps toward integrating this device with Rydberg-excited atoms. We have found that the nanoscale dielectric device creates a point-charge electric field that minimally perturbs ground-Rydberg qubit coherence at distances greater than 200 microns. Using the Rydberg blockade effect, we have created an entangled pair of atoms to perform entanglement-assisted sensing of the electric field to better understand its control. Overall, these experiments show how this nanophotonic device is a promising candidate to use as an optical interface for a Rydberg atom-based quantum computing node.
A leading strategy for the creation of a scalable quantum computer is through a networked architecture. This would comprise stationary nodes for quantum information processing and photonic channels for their communication and entanglement distribution. In this scheme a coherent interface between light and matter is a critical component, facilitating the deterministic and reversible transfer of quantum information between stationary and travelling qubits. This requirement may be fulfilled by a high finesse optical cavity, whose radiation field is strongly coupled to a trapped quantised emitter. Neutral atoms are an ideal species for the development of such a device, given their inherent compatibility with dielectric mirror surfaces. However, an outstanding challenge in building an elementary network of neutral atom-cavity systems is in establishing a single atom dipole trap within each cavity mode. This thesis presents the development of an open-access cavity suitable for single atom localisation, whilst maintaining strong atom-cavity coupling, {g0,κ,γ} = {11,2.1,3} × 2πMHz, and the efficient extraction of generated photons, η=0.5. We consider cavity design methodology, deriving a connection between the physical properties of the optical resonator and its intended role in the production of single photons. An experimental platform is developed for the creation of cavity mirrors by laser ablation, with a high degree of geometrical control. This is used to produce a set of pyramidal micro-mirrors, demonstrated to represent a favourable alternative to the widespread adoption of fibre-tip cavities. These pyramidal mirrors are shown to support multi-feature resonators, allowing several atom-cavity interfaces to be formed using a pair of substrates. By developing a novel procedure for mirror alignment, a hybrid mirror cavity is fabricated and integrated into an experimental architecture tailored for atomic trapping. Suitability of the cavity for future experimentation is demonstrated by frequency stabilisation to an atomic resonance of 87Rb.