Motivated to develop quantum technologies and to study ever-more complex quantum systems,scientists are developing increasingly sophisticated experimental tools to control and\nmeasure quantum samples such as ensembles of ultracold atoms. A high-finesse optical\ncavity can be used to measure the state of atoms within its photonic mode with precision\nlimited only by quantum uncertainty. Such a cavity can also be used to mediate interactions\nbetween different atoms within the cavity mode. High-resolution microscope objectives have\nbeen interfaced with ultracold atom experiments to allow researchers to image single atoms\nwithin optical lattices, to trap single atoms in microtweezer arrays, and to imprint arbitrary\noptical patterns onto atomic ensembles. Among other applications, these technologies have\nallowed researchers to investigate many-body quantum systems, engineer novel interactions,\nand realize high-fidelity quantum operations.This dissertation presents the details of the design, construction, and operation of a new, versatileatomic physics apparatus that combines these two experimental tools. The apparatus\nincludes a high-finesse optical cavity into which atoms are optically transported. In addition,\nthere is a high-numerical-aperture objective aligned to image, with micron-scale resolution,\natoms trapped within the center of the optical cavity. We present results demonstrating\nthe capability of this apparatus to deliver and study ultracold atomic samples, ranging from\nsingle atoms to Bose-Einstein condensates. We demonstrate a dispersive shift of the cavity\nresonance due to the presence of atoms in the cavity mode and the trapping and imaging of\nsingle atoms in optical microtweezers. We also present an atomic scanning probe microscopy\ntechnique with which a single atom in a microtweezer is used to map out the spatial amplitude\npattern of an optical cavity mode standing wave by monitoring the position-dependent\nscattering properties of the atom.
Motivated to develop quantum technologies and to study ever-more complex quantum systems,scientists are developing increasingly sophisticated experimental tools to control and\nmeasure quantum samples such as ensembles of ultracold atoms. A high-finesse optical\ncavity can be used to measure the state of atoms within its photonic mode with precision\nlimited only by quantum uncertainty. Such a cavity can also be used to mediate interactions\nbetween different atoms within the cavity mode. High-resolution microscope objectives have\nbeen interfaced with ultracold atom experiments to allow researchers to image single atoms\nwithin optical lattices, to trap single atoms in microtweezer arrays, and to imprint arbitrary\noptical patterns onto atomic ensembles. Among other applications, these technologies have\nallowed researchers to investigate many-body quantum systems, engineer novel interactions,\nand realize high-fidelity quantum operations.This dissertation presents the details of the design, construction, and operation of a new, versatileatomic physics apparatus that combines these two experimental tools. The apparatus\nincludes a high-finesse optical cavity into which atoms are optically transported. In addition,\nthere is a high-numerical-aperture objective aligned to image, with micron-scale resolution,\natoms trapped within the center of the optical cavity. We present results demonstrating\nthe capability of this apparatus to deliver and study ultracold atomic samples, ranging from\nsingle atoms to Bose-Einstein condensates. We demonstrate a dispersive shift of the cavity\nresonance due to the presence of atoms in the cavity mode and the trapping and imaging of\nsingle atoms in optical microtweezers. We also present an atomic scanning probe microscopy\ntechnique with which a single atom in a microtweezer is used to map out the spatial amplitude\npattern of an optical cavity mode standing wave by monitoring the position-dependent\nscattering properties of the atom.
We present and characterize an experimental system in which we achieve the integration of an ultrahigh finesse optical cavity with a Bose-Einstein condensate (BEC). The conceptually novel design of the apparatus for the production of BECs features nested vacuum chambers and an in vacuo magnetic transport configuration. It grants large scale spatial access to the BEC for samples and probes via a modular and exchangeable “science platform.” We are able to produce Rb87 condensates of 5×106 atoms and to output couple continuous atom lasers. The cavity is mounted on the science platform on top of a vibration isolation system. The optical cavity works in the strong coupling regime of cavity quantum electrodynamics and serves as a quantum optical detector for single atoms. This system enables us to study atom optics on a single particle level and to further develop the field of quantum atom optics. We describe the technological modules and the operation of the combined BEC cavity apparatus. Its performance is characterized by single atom detection measurements for thermal and quantum degenerate atomic beams. The atom laser provides a fast and controllable supply of atoms coupling with the cavity mode and allows for an efficient study of atom field interactions in the strong coupling regime. Moreover, the high detection efficiency for quantum degenerate atoms distinguishes the cavity as a sensitive and weakly invasive probe for cold atomic clouds.
Cavity quantum electrodynamics (QED) studies the interaction between atoms and a single electromagnetic mode. When the atoms form a degenerate quantum gas, the resulting lightâ matter interaction reflects the underlying quantum statistics of the particles. Recently, degenerate Fermi gases have been coupled to optical cavities, enabling the exploration of strongly correlated fermionic systems with interactions mediated by cavity photons. Remarkably, when disorder is introduced into such systems, the resulting model realizes fermions with random, long-range interactions characteristic of the Sachdevâ Yeâ Kitaev Hamiltonian. This platform therefore offers a possible route toward the experimental investigation of holographic duality, linking strongly interacting quantum matter to black hole physics through the AdS/CFT correspondence. As a step toward realizing this model, we developed a new technology: the cavity microscope. This device combines the strong light-matter coupling of cavity QED with the micrometer-scale spatial resolution provided by high-numerical-aperture optics. This thesis presents the operation and the first experimental results obtained with this new platform. First, the high-resolution addressing capability of the cavity microscope was used to locally modify the level structure of thermal atoms within the cavity mode. This allowed us to extract spatially resolved information about the atomic density from a global cavity measurement. In doing so, we overcome a longstanding limitation of cavity QED experiments, where the spatial structure of the light-matter interaction is typically fixed by the cavity mode and cannot be freely tuned. Second, we implemented a tightly focused optical trap that enabled the extraction of a small degenerate Fermi gas from a larger atomic cloud, coupled to the cavity mode. We then systematically investigated the light-matter interaction between this tweezer-trapped Fermi gas and the cavity mode by studying the superradiant phase transition of atoms in the cavity. We find that the transition can be either facilitated or suppressed by the fermionic occupation of phase space. The crossover between these two regimes occurs when the scattering wavevector becomes approximately twice the Fermi wavevector, revealing the crucial role of Fermi statistics in cavity-mediated interactions. These results pave the way toward the deterministic preparation of few-fermion systems inside an optical cavity, enabling the study of finite-size and trap-filling effects in cavity QED. In an upgraded version of the cavity microscope, the number of atoms can approach the cavity cooperativity, bringing the system into a new regime where entanglement can extend across the entire ensemble. Finally, by introducing time-dependent randomization of cavity-mediated interactions, this platform could realize low-rank SYK models, opening the door to experimental investigations of fast scrambling, thermalization, and quantum chaos in strongly interacting quantum matter.
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.
Cavity quantum electrodynamics offers the possibility of observing and controlling the motion of a few or individual atoms, enabling the realization of various quantum technological tasks such as quantum enhanced metrology or quantum simulation of strongly correlated matter. A core limitation of these experiments lies in the mode structure of the cavity field, which is hard coded in the shape and geometry of the mirrors. As a result, most applications of cavity QED trade spatial resolution for enhanced sensitivity. Here, we propose and demonstrate a cavity-microscope device capable of controlling in space and time the coupling between atoms and light in a single-mode high-finesse cavity, reaching a spatial resolution an order of magnitude lower than the cavity-mode waist. This is achieved through local Floquet engineering of the atomic level structure, imprinting a corresponding atom-field coupling. We illustrate this capability by engineering micrometer-scale coupling, using cavity-assisted atomic measurements and optimization. Our system forms an optical device with a single optical axis, has the same footprint and complexity as a standard Fabry-Perot cavity or confocal lens pair, and can be used for any atomic species. This technique opens a wide range of perspectives, from ultrafast cavity-enhanced midcircuit readout to the quantum simulation of fully connected models of quantum matter such as the Sachdev-Ye-Kitaev model. Published by the American Physical Society 2024
We present the design and assembly of a cavity microscope for quantum simulations with ultracold atoms. The system integrates a high-finesse optical cavity with a pair of high-numerical aperture lenses sharing a common optical axis, enabling simultaneous operation with light close-to-atomic resonance. The system keeps the advantages of a rigid, single-block structure holding the lenses and cavity together, and improves over existing designs by using most of the solid angle left free by the cavity mode for imaging and atomic manipulation purposes. The cavity has a length of 19.786 mm, a finesse of 2.35 × 10 4 and operates 214 µm away from the concentric limit, deep in the strong coupling regime. The two lenses offer a numerical aperture of 0.52 each and maximal optical access in all directions transverse to the cavity axis, compatible with applications in quantum-gas microscopes, micro-tweezer arrays or few-fermions systems, as well as future cavity-assisted quantum simulation protocols demanding sub-cavity-mode control of the atom-cavity coupling.
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.