Abstract Integrated quantum photonics enables the generation, manipulation, and detection of quantum states of light in miniaturized waveguide circuits. Implementation of these three operations in a single integrated platform is a crucial step toward a fully scalable approach to quantum photonic technologies. In this context, diamond has emerged as a particularly promising material as it naturally combines a large transparency range for the fabrication of low‐loss photonic circuits, and a variety of optically active defects for the realization of efficient single‐photon emitters. Furthermore, its high Young's modulus makes it ideal for the implementation of tunable optomechanical devices for active quantum state manipulation. This review reports recent progress on the realization of the main components required for a diamond‐based integrated quantum photonic architecture: single‐photon emitters, static and actively tunable waveguide circuits, and, as a last building block, integrated superconducting single‐photon detectors.
Abstract Integrated quantum photonics enables the generation, manipulation, and detection of quantum states of light in miniaturized waveguide circuits. Implementation of these three operations in a single integrated platform is a crucial step toward a fully scalable approach to quantum photonic technologies. In this context, diamond has emerged as a particularly promising material as it naturally combines a large transparency range for the fabrication of low‐loss photonic circuits, and a variety of optically active defects for the realization of efficient single‐photon emitters. Furthermore, its high Young's modulus makes it ideal for the implementation of tunable optomechanical devices for active quantum state manipulation. This review reports recent progress on the realization of the main components required for a diamond‐based integrated quantum photonic architecture: single‐photon emitters, static and actively tunable waveguide circuits, and, as a last building block, integrated superconducting single‐photon detectors.
Diamond has emerged as an optimal platform for the realization of fully integrated quantum photonic technologies. In the cover image, a set of electrically tunable color centers supply a source of indistinguishable single photons in different diamond waveguides; a network of directional couplers and opto-mechanical phase shifters is employed for active manipulation of quantum states of light, which are detected at the output of the circuit by integrated superconducting single photon detectors. For further details see the Review (article number 1800061) by Wolfram Pernice and co-workers.
Photonic quantum technologies hold promise to repeat the success of integrated nanophotonic circuits in non-classical applications. Using linear optical elements, quantum optical computations can be performed with integrated optical circuits and can therefore overcome the existing limitations in terms of scalability. In addition to passive optical devices for realizing photonic quantum gates, active elements, such as single-photon sources and single-photon detectors, are essential ingredients for future optical quantum circuits. Material systems that allow for the monolithic integration of all components are particularly attractive, including III-V semiconductors, silicon and diamond. Here, we demonstrate nanophotonic integrated circuits made from high-quality polycrystalline diamond thin films in combination with on-chip single-photon detectors. By using superconducting nanowires that are coupled evanescently to traveling waves, we achieve high detection efficiencies of up to 66% as well as low dark count rates and a timing resolution of 190 ps. Our devices are fully scalable and hold promise for functional diamond photonic quantum devices. The development of on-chip quantum circuitry progresses with the integration of single-photon detectors with diamond nanophotonic waveguides. Researchers based in Germany at Karlsruhe Institute of Technology and the Fraunhofer Institute of Applied Solid State Physics have fabricated superconducting niobium nitride nanowire detectors directly on top of diamond rib waveguides. This traveling wave design means that photons propagating in the diamond waveguides are coupled evanescently to the superconducting nanowires, allowing efficent on-chip detection of single photons. The small footprints of the detectors allow hundreds of detector circuits to be realized on a single chip. Furthermore, their fast response (they have a decay time of just 5.1 nanoseconds) allows operation at count rates of up to 200 megahertz and with a timing resolution of 190 picoseconds.
Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2,3]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [4]), measurement (eg. [5]) and other quantum technologies [6]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [7]. Here we report high-fidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [8]. We have demonstrated controlled manipulation of up to four photons on-chip, including highfidelity single qubit operations, using a lithographically patterned resistive phase shifter [9]. We have used this architecture to implement a small-scale compiled version of Shor's quantum factoring algorithm [10], demonstrated heralded generation of tunable four photon entangled states from a six photon input [11], a reconfigurable two-qubit circuit [12], and combined waveguide photonic circuits with superconducting single photon detectors [13]. We describe complex quantum interference behavior in multi-mode interference devices with up to eight inputs and outputs [14], and quantum walks of correlated particles in arrays of coupled waveguides [15]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [16,17] and diamond [18,19] and nonlinear [20,21] photon sources.
Integrated photonic devices in diamond have tremendous potential for many quantum applications, including long-distance quantum communication, quantum information processing, and quantum sensing. These devices benefit from diamond's combination of exceptional thermal, optical, and mechanical properties. Its wide electronic bandgap makes diamond an ideal host for a variety of optical active spin qubits that are key building blocks for quantum technologies. In landmark experiments, diamond spin qubits have enabled demonstrations of remote entanglement, memory-enhanced quantum communication, and multi-qubit spin registers with fault-tolerant quantum error correction, leading to the realization of multinode quantum networks. These advances put diamond at the forefront of solid-state material platforms for quantum information processing. Recent developments in diamond nanofabrication techniques provide a promising route to further scaling of these landmark experiments towards real-life quantum technologies. In this paper, we focus on the recent progress in creating integrated diamond quantum photonic devices, with particular emphasis on spin-photon interfaces, cavity optomechanical devices, and spin-phonon transduction. Finally, we discuss prospects and remaining challenges for the use of diamond in scalable quantum technologies.
Very recently, the interest for quantum technologies by the scientific community and industry has strongly increased. Different types of implementations have been proposed as a practical implementation for a quantum bit. In particular, quantum photonics is a strong candidate for such applications. We are interested in using single photons and single spins in diamond as a solid state host matrix (nanodiamonds or membranes). Integration of nanosources of light is currently a major bottleneck preventing the realisation of all-photonic chips for quantum technologies and nanophotonics applications. Ideally, one needs optical circuitry, on-chip photodetection and on-chip generation of quantum states of light (single photons, entangled photons…). Our recent work on a new platform for quantum photonics using integrated optics can offer an easier and robust way to create compact quantum circuits that can be on chip and scalable. In this context, the coupling between waveguides and single photon emitters is critical. The goal of our research is to efficiently couple single photon emitters with a new platform made of optical glass waveguides. These waveguides are based on the so-called ion-exchange glass technology and is know in the photonics industry for quite some time but has never been used in the context of quantum technologies. Efficient light-matter interface is of primordial importance in this system. To achieve this goal, several paths are undertaken such as the use of dielectric and plasmonic structuration in order to increase the light interaction with the waveguide or to develop fabrication techniques to insert the emitters directly inside the guide (for nanodiamonds). We will show what is our current state of the art for placing single emitters at the right place on our optical waveguides made of ion-exchange in glass and in particular what can be done to improve our first promising results in order to get near unity coupling between the optical bus and single photon emitters. We will show first results with semiconductor nanocrystals (NCs) but also using nitrogen-vacancy and silicon-vacancy defects in nanodiamond. The very first step in of our approach consists in the design of the structured waveguide using electromagnetic FDTD. We demonstrated that it is possible to achieve more than 90% coupling. In practice, before using coloured centres in diamond, we started working with CdSe/ZnS semiconductor nanocrystals. So far, we use straight waveguides defined to be single modes at the nominal wavelength of the emission line of the nanoemitters. The positioning of nanoemitters is still a challenge to be achieved. We developed an original technique based on photopolymerisation of light where the nanocrystals are grafted into a light sensitive polymer and can be placed at adequate positions.
Integrated photonics provides a powerful approach for developing compact, stable and scalable architectures for the generation, manipulation and detection of quantum states of light. To this end, several material platforms are being developed in parallel, each providing its specific assets, and hybridization techniques to combine their strengths are now possible. This review focuses on AlGaAs, a III-V semiconductor platform combining a mature fabrication technology, direct band-gap compliant with electrical injection, low-loss operation, large electro-optic effect, and compatibility with superconducting detectors for on-chip detection. We detail recent implementations of room-temperature sources of quantum light based on the high second- and third-order optical nonlinearities of the material, as well as photonic circuits embedding various functionalities ranging from polarizing beamsplitters to Mach-Zehnder interferometers, modulators and tunable filters. We then present several realizations of quantum state engineering enabled by these recent advances and discuss open perspectives and remaining challenges in the field of integrated quantum photonics with AlGaAs.