We develop a general framework for the analysis of two-sided quantum interfaces, composed of collections of atoms interacting with paraxial light. Accounting for photon-mediated dipole-dipole interactions, our approach is based on the mapping of collective atom-photon interfaces onto a generic one-dimensional model of light scattering, characterized by a reflectivity parameter r 0 . This entails two key practical advantages: (i) the efficiency of the quantum interface in performing various quantum tasks, such as quantum memory or entanglement generation, is universally given by r 0 and is hence reduced to a measurement or classical calculation of a reflectivity; (ii) the efficiency can be greatly enhanced by a properly designed photon mode that spatially matches a collective-dipole eigenmode of the atoms. We demonstrate our approach for realistic cases of finite-size atomic arrays, partially filled arrays, and circular arrays. This provides a unified approach for treating collective light-matter coupling in various platforms, such as optical lattices and optical tweezers. Published by the American Physical Society 2024
We develop a general framework for the analysis of two-sided quantum interfaces, composed of collections of atoms interacting with paraxial light. Accounting for photon-mediated dipole-dipole interactions, our approach is based on the mapping of collective atom-photon interfaces onto a generic one-dimensional model of light scattering, characterized by a reflectivity parameter r 0 . This entails two key practical advantages: (i) the efficiency of the quantum interface in performing various quantum tasks, such as quantum memory or entanglement generation, is universally given by r 0 and is hence reduced to a measurement or classical calculation of a reflectivity; (ii) the efficiency can be greatly enhanced by a properly designed photon mode that spatially matches a collective-dipole eigenmode of the atoms. We demonstrate our approach for realistic cases of finite-size atomic arrays, partially filled arrays, and circular arrays. This provides a unified approach for treating collective light-matter coupling in various platforms, such as optical lattices and optical tweezers. Published by the American Physical Society 2024
We consider the coupling of light, via an optical cavity, to two-dimensional atomic arrays whose lattice spacing exceeds the wavelength of the light. Such “superwavelength” spacing is typical of optical tweezer arrays. While subwavelength arrays exhibit strong atom-photon coupling, characterized by high optical reflectivity in free space, the coupling efficiency of superwavelength arrays is reduced due to collective scattering losses to high diffraction orders. We show how a moderate-finesse cavity can overcome these losses. As the scattering losses peak at certain discrete values of the lattice spacing, the spacing can be optimized to achieve efficient atom-photon coupling in the cavity. Our cavity-QED theory properly accounts for collective dipolar interactions mediated by the lossy, non-cavity-confined photon modes and for finite-size effects of both the array and the light field. These findings pave the way to harnessing the versatility of tweezer arrays for efficient atom-photon interfaces in applications of quantum computing, networking, and nonlinear optics. Published by the American Physical Society 2024
Recent experimental advances in preparing regular defect-free 2D arrays of atoms with optical traps have offered new opportunities to engineer strong collective couplings between light and atoms as quantum optical dipoles. Applications of such collective light-matter interactions include the realization of atom-thick mirrors, retrieval of quantum memories with high efficiency, or the implementation of topological quantum optics. I will present novel applications in the context of quantum networking. First, I will discuss the design of a chiral photonic quantum link, where distant single atoms interact by exchanging photons propagating in a unique direction in free space. This is achieved by coupling both single atoms, representing qubits implemented using a pair of Rydberg states, to bi-layer atomic arrays which act as quantum phased-array antennas. Exploiting the combination of a “Rydberg-dressing” laser and a control laser driving the atomic arrays, an effective Rydberg dipole-dipole interaction can be engineered between atoms and atomic arrays as quantum emitters, allowing to match the spatial modes of spontaneously emitted and absorbed photons to a Gaussian mode of interest. In this way, we realize a chiral quantum interface, i.e., where atoms couple to photonic modes with a unique direction of propagation. This setup provides a basic building block of a novel platform for quantum networks in free space, i.e., without requiring coupling atoms to modes of cavities or nanostructures, which I will illustrate with the deterministic coherent transfer of quantum states between single atoms with high fidelity. Second, I will discuss the collective radiation properties of two distant single-layer atomic arrays acting as quantum memories. This system can support a long-lived non-local superposition state of atomic excitations exhibiting strong subradiance. This “dark” mode consists of an atomic excitation which is delocalized between the two distant atomic arrays, in such a way that the overall radiation is strongly suppressed by quantum interference. I will describe the preparation of these states and their application as resource of non-local entanglement. In particular, by weakly driving the arrays, the state of the quantum memories, localized in each array, can be transferred to this “non-local” subradiant state, allowing again for a deterministic coherent quantum state transfer with high fidelity between the memories. Finally, I will discuss experimental realizations using cold atoms in optical trap arrays, and the effect of experimental imperfections in the arrays, such as finite defect probability, temperature, and depth of the optical traps.
We consider quantum light-matter interfaces comprised of multiple layers of two-dimensional tweezer atomic arrays, wherein the lattice spacings exceed the wavelength of light. While the coupling of light to a single layer of such a "superwavelength" lattice is considerably reduced due to scattering losses to high diffraction orders, we show that the addition of layers can suppress these losses through destructive interference between the layers. Mapping the problem to a 1D model of a quantum interface wherein the coupling efficiency is characterized by a reflectivity, we analyze the latter by developing a geometrical optics formulation, accounting for realistic finite-size arrays. We find that optimized efficiency favors small diffraction-order angles and small interlayer separations, and that the coupling inefficiency for two layers universally scales as N^{-1} with the atom number per layer N. We validate our predictions using direct numerical calculations of the scattering reflectivity and the performance of a quantum memory protocol, demonstrating high atom-photon coupling efficiency. This opens the way for various applications in tweezer atomic-array platforms.
Summary form only given. Developing light-matter interfaces is a crucial capability with unique applications to quantum optics and quantum information networks [1]. In this context, our group focuses on the study of interactions between photons guided by nanoscale waveguides and arrays of trapped atoms. Nanoscale waveguides offer a compelling platform because of the tight transverse confinement of the propagating light, the strong photon-atom coupling in single pass, and the potential long-range atom-atom interaction mediated by the guided photons [2]. Our platform, based on an optical nanofiber, already allowed the demonstration of an all-fibered optical memory with a storage and retrieval efficiency ri = 10% and a high SNR at the single photon level [3]. Then, by using an optical lattice in the evanescent field surrounding the nanofiber with a period close to commensurate with the resonant wavelength, we demonstrated large Bragg reflection by the 1D array of trapped atoms [4].
Subwavelength arrays of quantum emitters offer an efficient free-space approach to coherent light-matter interfacing, using ultracold atoms or two-dimensional solid-state quantum materials. The combination of collectively suppressed photon losses and emerging optical nonlinearities due to strong photon coupling to mesoscopic numbers of emitters holds promise for generating nonclassical light and engineering effective interactions between freely propagating photons. While most studies have thus far relied on numerical simulations, we describe here a diagrammatic Green's function approach that permits analytical investigations of nonlinear processes. We illustrate the method by deriving a simple expression for the scattering matrix that describes photon-photon interactions in an extended two-dimensional array of quantum emitters and reproduces the results of numerical simulations of coherently driven arrays. The approach yields intuitive insights into the nonlinear response of the system and offers a promising framework for the systematic development of a theory for interacting photons and many-body effects on collective radiance in two-dimensional arrays of quantum emitters. Published by the American Physical Society 2024
We study quantum light-matter interfaces based on bilayer atomic arrays in free space, considering interlayer spacings az that may deviate from the Bragg-symmetric condition, az∈integer×λ/2 with λ the light wavelength. Mapping the problem to a one-dimensional model, we show that the interface efficiency is fully determined by simple scattering observables − reflection and transmission − providing a direct, experimentally accessible characterization. This reveals new opportunities for optimizing light-matter coupling by operating beyond the Bragg symmetry. In particular, we identify configurations that suppress diffraction losses via destructive interference, enabling substantially improved interface efficiencies compared to Bragg-constrained designs. In addition, we introduce a new quantum memory scheme based on a collective dark state whose coupling to light is continuously controlled by tuning the interlayer spacing. More broadly, our results establish non-symmetric atomic arrays as a flexible platform for efficient quantum interfaces in free space.