Cavity quantum electrodynamics (QED) with cooperativity far greater than unity enables high-fidelity quantum sensing and information processing.The high-cooperativity regime is often reached through the use of short single-mode resonators.More complicated multimode resonators, such as the near-confocal optical Fabry-Pérot cavity, can provide intracavity atomic imaging in addition to high cooperativity.This capability has recently proved important for exploring quantum many-body physics in the driven-dissipative setting.In this work, we show that a confocal-cavity-QED microscope can realize cooperativity in excess of 110.This cooperativity is on par with the very best single-mode cavities (which are far shorter) and 21 times greater than single-mode resonators of similar length and mirror radii.The 1.7-µm imaging resolution is naturally identical to the photon-mediated interaction range.We measure these quantities by determining the threshold of cavity superradiance when small optically tweezed Bose-Einstein condensates are pumped at various intracavity locations.Transmission measurements of an ex situ cavity corroborate these results.We provide a theoretical description that shows how cooperativity enhancement arises from the dispersive coupling to the atoms of many near-degenerate modes.
Cavity quantum electrodynamics (QED) with cooperativity far greater than unity enables high-fidelity quantum sensing and information processing.The high-cooperativity regime is often reached through the use of short single-mode resonators.More complicated multimode resonators, such as the near-confocal optical Fabry-Pérot cavity, can provide intracavity atomic imaging in addition to high cooperativity.This capability has recently proved important for exploring quantum many-body physics in the driven-dissipative setting.In this work, we show that a confocal-cavity-QED microscope can realize cooperativity in excess of 110.This cooperativity is on par with the very best single-mode cavities (which are far shorter) and 21 times greater than single-mode resonators of similar length and mirror radii.The 1.7-µm imaging resolution is naturally identical to the photon-mediated interaction range.We measure these quantities by determining the threshold of cavity superradiance when small optically tweezed Bose-Einstein condensates are pumped at various intracavity locations.Transmission measurements of an ex situ cavity corroborate these results.We provide a theoretical description that shows how cooperativity enhancement arises from the dispersive coupling to the atoms of many near-degenerate modes.
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
From fundamental studies of light-matter interaction to applications in quantum networking and sensing, cavity quantum electrodynamics (QED) provides a toolbox to control interactions between atoms and photons. The coherence of interactions is determined by the single-pass atomic absorption and number of photon round-trips. Reducing the cavity loss has enabled resonators supporting 1 million roundtrips but with limited material choices and increased alignment sensitivity. Here, we present a high–numerical aperture, lens-based resonator that pushes the single-atom single-photon absorption probability near its fundamental limit, reducing the mode size at the atom to order λ. This resonator provides a single-atom cooperativity of 1.6 in a cavity where the light circulates ∼10 times. We load single 87 Rb atoms into this cavity, observe strong coupling, and demonstrate cavity-enhanced atom detection with fidelity of 99.55(6)% and survival of 99.89(4)% in 130 μs. Introducing intracavity imaging systems will enable cavity arrays compatible with Rydberg atom array computing technologies, expanding the applicability of the cavity QED toolbox.
We present a novel cavity QED system in which a Bose–Einstein condensate (BEC) is trapped within a high-finesse optical cavity whose length may be adjusted to access both single-mode and multimode configurations. We demonstrate the coupling of an atomic ensemble to the cavity in both configurations and measure that the single-atom, -mode cooperativity exceeds unity. The atoms are confined either within an intracavity far-off-resonance optical dipole trap or a crossed optical dipole trap via transversely oriented lasers. Multimode cavity QED provides fully emergent and dynamical optical lattices for intracavity BECs, in that the process of atomic self-organization may be described as a continuous symmetry breaking phase transition resulting in the emergence of a compliant lattice with phonon-like excitations. Such systems will enable explorations of quantum soft matter, including superfluid smectics, superfluid glasses, and spin glasses as well as neuromorphic associative memory.
Neutral-atom array and cavity quantum electrodynamics offer complementary strengths for quantum science: scalable, reconfigurable qubit architectures and strong coherent light-matter coupling. Combining them in a single platform requires an optical cavity with simultaneously high cooperativity, sufficient mode volume to accommodate atom array, and ample side optical access for atom trapping, imaging, cooling, and rearrangement, a combination that is challenging to achieve. Here we realize an atomic array integrated with a millimeter-scale Fabry--Pérot cavity whose optically-characterized single-atom cooperativity reaches ηcav=125±13. Atom-cavity transmission spectra of trapped atoms yield an effective spectroscopic cooperativity ηspec=106±3, providing an in-situ verification of strong coupling in the integrated platform. In this integrated system, we achieve a state-measurement fidelity of 99.925−18+15% for a single atom with a 4-μs readout time. We also demonstrate simultaneous coupling of up to 21 individually trapped atoms to the antinode of the cavity mode. The key technical advance is a two-step mirror-fabrication method combining precision mechanical shaping and carbon-dioxide laser polishing, which produces concave fused-silica mirrors with sub-millimeter radii of curvature and residual roughness below 2A˚. Our results establish a regime of cavity-integrated atomic array that simultaneously provides high cooperativity, large mode volume, and flexible manipulation of individual atoms, opening opportunities for cavity-assisted quantum state readout and long-range entanglement-engineering in atom-array platforms.
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.
A central challenge for cavity-QED-based quantum technologies is to make high-cooperativity optical interfaces compatible with site-resolved arrays of single atoms. Here, we demonstrate optical tweezer arrays of individual 87Rb atoms inside a fiber Fabry-Perot microcavity with single-atom cooperativity C∼90. We combine background-free site-resolved fluorescence imaging of extended arrays with collective coupling to a common cavity mode for arrays with a mean atom number up to Nˉ≃36. These results establish a high-cooperativity platform for many-body cavity-QED with site-resolved detection and control.