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The scaling of many photonic quantum information processing systems is ultimately limited by the flux of quantum light throughout an integrated photonic circuit. Source brightness and waveguide loss set basic limits on the on-chip photon flux. While substantial progress has been made, separately, towards ultra-low loss chip-scale photonic circuits and high brightness single-photon sources, integration of these technologies has remained elusive. Here, we report the integration of a quantum emitter single-photon source with a wafer-scale, ultra-low loss silicon nitride photonic circuit. We demonstrate triggered and pure single-photon emission into a Si3N4 photonic circuit with ≈ 1 dB/m propagation loss at a wavelength of ≈ 930 nm. We also observe resonance fluorescence in the strong drive regime, showing promise towards coherent control of quantum emitters. These results are a step forward towards scaled chip-integrated photonic quantum information systems in which storing, time-demultiplexing or buffering of deterministically generated single-photons is critical.

Integrated photonics is at the heart of many classical technologies, fromoptical communications to biosensors, LIDAR, and data center fiberinterconnects. There is strong evidence that these integrated technologies willplay a key role in quantum systems as they grow from few-qubit prototypes totens of thousands of qubits. The underlying laser and optical quantumtechnologies, with the required functionality and performance, can only berealized through the integration of these components onto quantum photonicintegrated circuits (QPICs) with accompanying electronics. In the last decade,remarkable advances in quantum photonic integration and a dramatic reduction inoptical losses have enabled benchtop experiments to be scaled down to prototypechips with improvements in efficiency, robustness, and key performance metrics.The reduction in size, weight, power, and improvement in stability that will beenabled by QPICs will play a key role in increasing the degree of complexityand scale in quantum demonstrations. In the next decade, with sustainedresearch, development, and investment in the quantum photonic ecosystem (i.e.PIC-based platforms, devices and circuits, fabrication and integrationprocesses, packaging, and testing and benchmarking), we will witness thetransition from single- and few-function prototypes to the large-scaleintegration of multi-functional and reconfigurable QPICs that will define howinformation is processed, stored, transmitted, and utilized for quantumcomputing, communications, metrology, and sensing. This roadmap highlights thecurrent progress in the field of integrated quantum photonics, futurechallenges, and advances in science and technology needed to meet thesechallenges.

Integrated photonics is at the heart of many classical technologies, fromoptical communications to biosensors, LIDAR, and data center fiberinterconnects. There is strong evidence that these integrated technologies willplay a key role in quantum systems as they grow from few-qubit prototypes totens of thousands of qubits. The underlying laser and optical quantumtechnologies, with the required functionality and performance, can only berealized through the integration of these components onto quantum photonicintegrated circuits (QPICs) with accompanying electronics. In the last decade,remarkable advances in quantum photonic integration and a dramatic reduction inoptical losses have enabled benchtop experiments to be scaled down to prototypechips with improvements in efficiency, robustness, and key performance metrics.The reduction in size, weight, power, and improvement in stability that will beenabled by QPICs will play a key role in increasing the degree of complexityand scale in quantum demonstrations. In the next decade, with sustainedresearch, development, and investment in the quantum photonic ecosystem (i.e.PIC-based platforms, devices and circuits, fabrication and integrationprocesses, packaging, and testing and benchmarking), we will witness thetransition from single- and few-function prototypes to the large-scaleintegration of multi-functional and reconfigurable QPICs that will define howinformation is processed, stored, transmitted, and utilized for quantumcomputing, communications, metrology, and sensing. This roadmap highlights thecurrent progress in the field of integrated quantum photonics, futurechallenges, and advances in science and technology needed to meet thesechallenges.

The inherent crystal anisotropy of hexagonal boron nitride (hBN) provides the ability to support hyperbolic phonon polaritons, that is, polaritons that can propagate with very large wave vectors within the material volume, thereby enabling optical confinement to exceedingly small dimensions. Indeed, previous research has shown that nanometer-scale truncated nanocone hBN cavities, with deep subdiffractional dimensions, support three-dimensionally confined optical modes in the mid-infrared. Because of optical selection rules, only a few of the many theoretically predicted modes have been observed experimentally via far-field reflection and scattering-type scanning near-field optical microscopy (s-SNOM). The photothermal induced resonance (PTIR) technique probes optical and vibrational resonances overcoming weak far-field emission by leveraging an atomic force microscope (AFM) probe to transduce local sample expansion caused by light absorption. Here we show that PTIR enables the direct observation of previously unobserved, dark hyperbolic modes of hBN nanostructures. Leveraging these optical modes and their wide range of angular and radial momenta could provide a new degree of control over the electromagnetic near-field concentration, polarization in nanophotonic applications.

The inherent crystal anisotropy of hexagonal boron nitride (hBN) provides the ability to support hyperbolic phonon polaritons, that is, polaritons that can propagate with very large wave vectors within the material volume, thereby enabling optical confinement to exceedingly small dimensions. Indeed, previous research has shown that nanometer-scale truncated nanocone hBN cavities, with deep subdiffractional dimensions, support three-dimensionally confined optical modes in the mid-infrared. Because of optical selection rules, only a few of the many theoretically predicted modes have been observed experimentally via far-field reflection and scattering-type scanning near-field optical microscopy (s-SNOM). The photothermal induced resonance (PTIR) technique probes optical and vibrational resonances overcoming weak far-field emission by leveraging an atomic force microscope (AFM) probe to transduce local sample expansion caused by light absorption. Here we show that PTIR enables the direct observation of previously unobserved, dark hyperbolic modes of hBN nanostructures. Leveraging these optical modes and their wide range of angular and radial momenta could provide a new degree of control over the electromagnetic near-field concentration, polarization in nanophotonic applications.

Multifocus microscopy (MFM) allows high-resolution instantaneous three-dimensional (3D) imaging and has been applied to study biological specimens ranging from single molecules inside cells nuclei to entire embryos. We here describe pattern designs and nanofabrication methods for diffractive optics that optimize the light-efficiency of the central optical component of MFM: the diffractive multifocus grating (MFG). We also implement a "precise color" MFM layout with MFGs tailored to individual fluorophores in separate optical arms. The reported advancements enable faster and brighter volumetric time-lapse imaging of biological samples. In live microscopy applications, photon budget is a critical parameter and light-efficiency must be optimized to obtain the fastest possible frame rate while minimizing photodamage. We provide comprehensive descriptions and code for designing diffractive optical devices, and a detailed methods description for nanofabrication of devices. Theoretical efficiencies of reported designs is ≈90% and we have obtained efficiencies of > 80% in MFGs of our own manufacture. We demonstrate the performance of a multi-phase MFG in 3D functional neuronal imaging in living C. elegans.