Sophie W. Ding, Chang Jin, Zixi Li, Nicholas Achuthan, Kazuhiro Kuruma, Xinghan Guo, Brandon Grinkemeyer, David D. Awschalom, Nazar Delegan, F. Joseph Heremans, Alexander A. High, Marko Loncar
physics.opticsquant-phSubmitted Mar 9, 2026• Announced Mar 10, 2026
Diamond photonics has enabled efficient interfaces for quantum memories and is predicted to be a critical component of quantum networks. However, scalable network architectures require spatial, temporal, and spectral control of photons, which relies on nonlinear and electro-optic functionalities that diamond alone cannot provide. Here, we demonstrate heterogeneous integration of a thin-film lithium niobate (TFLN) platform, which has strong chi-2 nonlinearity and electro-optic effects, with thin diamond films. We demonstrate high-Q diamond photonic crystal cavities (Q factors exceeding 5x10^4 at 735 nm) that are lithographically aligned with TFLN photonic backbone and critically coupled to it. This allows us to realize low-loss diamond-TFLN "escalators" (loss ~1 dB/coupler) that support efficient light transfer between them. At cryogenic temperatures (5K), we can collect photons emitted from silicon vacancies (SiVs) embedded within the diamond structure via the TFLN photonic circuit. This approach establishes a scalable route toward integrated photonic circuits for practical quantum networking and other technologies.
Diamond photonics has enabled efficient interfaces for quantum memories and is predicted to be a critical component of quantum networks. However, scalable network architectures require spatial, temporal, and spectral control of photons, which relies on nonlinear and electro-optic functionalities that diamond alone cannot provide. Here, we demonstrate heterogeneous integration of a thin-film lithium niobate (TFLN) platform, which has strong chi-2 nonlinearity and electro-optic effects, with thin diamond films. We demonstrate high-Q diamond photonic crystal cavities (Q factors exceeding 5x10^4 at 735 nm) that are lithographically aligned with TFLN photonic backbone and critically coupled to it. This allows us to realize low-loss diamond-TFLN "escalators" (loss ~1 dB/coupler) that support efficient light transfer between them. At cryogenic temperatures (5K), we can collect photons emitted from silicon vacancies (SiVs) embedded within the diamond structure via the TFLN photonic circuit. This approach establishes a scalable route toward integrated photonic circuits for practical quantum networking and other technologies.
The realization of quantum networks capable of distributing quantum information over kilometer scale distances is key to maximizing the potential of quantum information technology. Implementing this technology requires both the ability to generate remote entanglement between quantum memory nodes, requiring an efficient spin-photon interface, and the ability to efficiently scale the classical optical control and multiplexing optics within a given node. In this work, we develop integrated photonics platforms in diamond and thin film lithium niobate to address both of these issues. Together, these platforms provide the necessary ingredients to create large scale quantum networking technology. For the quantum network nodes, we extend previous results combining diamond nanophotonic resonators with the silicon-vacancy defect as a quantum networking platform. We demonstrate, for the first time, quantum entanglement between SiV quantum memories across 35km in a deployed fiber network. We also develop additional functionalities within the SiV platform including the incorporation of deterministic strain to increase defect yield and deterministic single photon generation with the SiV. In order to enable the scalable control and multiplexing of individual SiV centers necessary for realizing practical quantum network nodes, we develop a state-of-the-art electro-optics platform operating at visible wavelengths using thin film lithium niobate. We develop an understanding of fabrication induced losses at visible wavelengths in the platform and a variety of key devices in the platform including high-bandwidth, low-drive voltage amplitude and phase modulators, as well as high-efficiency off chip couplers. Utilizing this platform we perform ultra-high efficiency electro-optic frequency shifting, achieving a 15 GHz frequency shift with over 50% efficiency. Finally, using our measured device performance, we discuss and model how these devices can effectively multiplex SiV-based quantum nodes. Thus through these two platforms we have demonstrated the necessary ingredients to realize large-scale quantum network nodes.
On-chip photonic quantum circuits with integrated quantum memories have the potential to radically advance hardware for quantum information processing. In particular, negatively charged group-IV color centers in diamond are promising candidates for quantum memories as they combine long storage times with excellent optical emission properties and an optically addressable spin state. However, as a material, diamond lacks the many functionalities needed to realize scalable quantum systems. Thin-film lithium niobate (TFLN), in contrast, offers a number of useful photonic nonlinearities, including the electro-optic effect, piezoelectricity, and capabilities for periodically poled quasi-phase matching. Here, we present the highly efficient heterogeneous integration of diamond nanobeams containing negatively charged silicon-vacancy (SiV) centers with TFLN waveguides. We observe greater than 90% transmission efficiency between the diamond nanobeam and the TFLN waveguide on average across multiple measurements. By comparing saturation signal levels between confocal and integrated collection, we estimate a more than 10-fold increase in photon emission channeled into TFLN waveguides versus that channeled into out-of-plane collection channels. Our results constitute a key step for creating scalable integrated quantum photonic circuits that leverage the advantages of both diamond and TFLN materials.
Practical quantum networks will require multi-qubit quantum nodes. This in turn will increase the complexity of the photonic circuits needed to control each qubit and require strategies to multiplex memories. Integrated photonics operating at visible to near-infrared (VNIR) wavelength range can provide solutions to these needs. In this work, we realize a VNIR thin-film lithium niobate (TFLN) integrated photonics platform with the key components to meet these requirements, including low-loss couplers (<1 dB/facet), switches (>20 dB extinction), and high-bandwidth electro-optic modulators (>50 GHz). With these devices, we demonstrate high-efficiency and CW-compatible frequency shifting (>50% efficiency at 15 GHz), as well as simultaneous laser amplitude and frequency control. Finally, we highlight an architecture for multiplexing quantum memories and outline how this platform can enable a 2-order of magnitude improvement in entanglement rates over single memory nodes. Our results demonstrate that TFLN can meet the necessary performance and scalability benchmarks to enable large-scale quantum nodes.
Integrated quantum photonics holds significant promise for scalable photonic quantum information processing, quantum repeaters, and quantum networks, but its development is hindered by the mismatch between materials hosting high-quality quantum emitters and those compatible with mature photonic technologies. Heterogeneous integration offers a potential solution to this challenge, yet practical implementations have been limited by inevitable insertion losses at material interfaces. Here, we present a self-aligned heterogeneous quantum photonic integration approach that can deterministically achieve near-unity coupling efficiency at the interface. To showcase our approach, we demonstrate Purcell enhancement of a silicon vacancy (SiV) center in diamond induced by a heterogeneous photonic crystal cavity defined by titanium dioxide (TiO2), as well as optical spin control and readout via a TiO2 photonic circuit. We further show that, when combined with inverse photonic design, our approach enables efficient and broadband collection of single photons from a color center into a heterogeneous waveguide. Our approach is not restricted to SiV centers or TiO2; it can be broadly applied to integrate diverse solid-state quantum emitters with thin-film photonic devices where conformal deposition is possible. Together, these results establish a practical route to scalable quantum photonic integrated circuits that combine high-quality quantum emitters with technologically mature photonic platforms.
Integrated thin-film lithium niobate (TFLN) photonics has emerged as a powerful platform for quantum information science, offering its outstanding nonlinear, electro-optic (EO), and integration capabilities. In this review, we present the latest advances in TFLN-based integrated photonics tailored to quantum technologies. We first explore state-of-the-art quantum light sources realized in both straight waveguide and resonator configuration, including high-brightness photon pair generations, squeezed light, and versatile entanglement schemes. Next, we detail progress in integrated photonic processors, with a focus on programmable interferometric networks, ultrafast EO modulators, and essential passive components for photonic qubit processing. We then address critical challenges in optical interfacing and detection technologies, discussing recent innovations in low-loss fiber-to-chip and grating coupler designs, as well as the integration of on-chip single photon detectors. This review provides a forward-looking perspective on scalable quantum photonic systems that could underpin future advances in quantum communication, computing, and sensing.
Photonic integrated circuits operating at cryogenic temperatures are necessary for many quantum technologies such as quantum transduction, integrated single-photon emitters and detectors, as well as deep-space communication and sensing devices. Thin-film lithium niobate (TFLN) is an emerging platform that is a strong candidate for fully integrated quantum photonics, offering low loss, fast electro-optic reconfigurability, nonlinear quantum light sources, and the ability to host quantum emitters and single-photon detectors. To interface TFLN with technologies that require cryogenic operation, like superconducting single-photon detectors, microwave-to-optical transducers, and solid-state quantum emitters, it is important to study its optical and electrical properties from room temperature down to cryogenic temperatures. Here, we investigate linear and nonlinear photonic devices, including racetrack resonators, Mach-Zehnder modulators and periodically poled waveguides in TFLN using a cryogenic fiber probe station with full temperature control down to 5 K. We quantify a shift in resonances, a 22% increase in electro-optic modulator half-wave voltage, a blue shift of 18 nm for Type-0 phase-matching as well as a red shift of 64 nm for Type-II phase-matching as the sample temperature decreases. Our study of nonlinear processes in a cryogenic environment will contribute towards developing novel devices for inter-platform quantum information processing, secure communication, and enhanced sensing.