From Atomic Defects to Integrated Photonics: A Perspective on Solid-State Quantum Light Sources

TL;DR

The article addresses how solid-state single-photon emitters (SPEs) across 0D–3D materials can be integrated with low-loss photonic circuits to enable scalable quantum photonic technologies. It surveys material platforms and integration strategies, highlighting trade-offs in operating temperature, coherence, Purcell enhancement, and coupling efficiency, and discusses concrete demonstrations in quantum sensing, quantum communication, and photonic quantum computing, as well as quantum AI approaches. By detailing transfer, wafer bonding, monolithic integration, pick-and-place assembly, doping/implantation, and photonic interconnects, the work outlines practical pathways toward heterogeneous, wafer-scale SPE integration on ultra-low-loss photonic chips. The findings underscore a practical route to large-scale quantum photonic systems through thoughtful material choice and hybrid integration, enabling on-chip sources that meet the demands of sensing, networking, and computation.

Abstract

Single-photon emitters (SPEs) constitute a foundational resource for quantum technologies, including secure communication, photonic quantum computing, and emerging quantum network architectures. A wide range of quantum materials, from atom-like point defects in bulk crystals to excitonic states in low-dimensional semiconductors, now provide bright, coherent, and scalable sources of non-classical light. Meanwhile, advances in photonic integration have enabled efficient routing, filtering, and on-chip manipulation of these emitters. From this perspective, we survey and discuss the technological landscape in which solid-state emitters interface with quantum sensing, quantum communication, quantum computation, and emerging photonic AI platforms. Further, we discuss the materials landscape underpinning modern single-photon sources from the zero-dimensional, one-dimensional, two-dimensional and three-dimensional materials. Lastly, we highlight key integration pathways for these single-photon emitters into scalable quantum photonic systems.

Figures (3)

• Figure 1: Outlook and applications of integrated single-photon emitter technology. Schematic overview of emerging directions where integrated single-photon emitters underpin quantum sensing, communication, and computing. (a) Quantum sensing High-brightness, high-purity single-photon emission engineered via cavity quantum electrodynamics, illustrated in the context of a long-baseline quantum sensor network of 15 GPS-synchronized atomic magnetometers in two multi-layer mu-metal shield rooms in Suzhou and Harbin (separation $\sim$1700 km), where wall-mounted zero-field magnetometers detect dark-photon–induced radio-frequency magnetic fields with femtotesla sensitivity. (b) Quantum-secured communication Integrated single-photon sources for on-chip quantum key distribution, where a strain-engineered WSe$_2$ monolayer in a closed-cycle cryostat (Alice) is pumped by a pulsed diode laser, spectrally filtered, polarization-controlled, and fiber-coupled to send BB84 polarization states (H, V, D, A) through a variable-loss channel to a four-state polarization analyzer (Bob); spectra isolating an 807 nm emission line and second-order autocorrelation histograms up to 10 MHz confirm low-noise, high-purity operation suitable for high-speed quantum links. (c) Photonic quantum computing and quantum AI Integration of indistinguishable quantum-dot emitters in reconfigurable photonic circuits, exemplified by a GaAs/InAs QD single-photon source on an ultra-low-loss Si$_3$N$_4$ waveguide feeding a 50:50 MMI splitter and exhibiting high-purity $g^{(2)}(\tau)$ under resonant excitation (right panel). Other hand a quantum optical reservoir computing (QORC) architecture that encodes classical data onto multimode single-photon resource states via random interferometric networks and linear optics, and shows enhanced classification performance when driven by single photons compared to coherent light (left panel). All figures are adapted with permission from: (a) ref. Jiang2024; (b) ref. Gao2023; (c) ref. Sakurai:25Chanana2022ULLW.
• Figure 2: Materials landscape of integrated quantum light sources across dimensions (a) Electrically controlled InAs quantum dot embedded in a GaAs nanophotonic waveguide with adiabatic coupling to an on-chip output, exemplifying a zero-dimensional emitter engineered into a bright, nearly deterministic single-photon source via a large $\beta$-factor and charge stability. (b) Doped single-walled carbon nanotube (SWCNT) hosting $sp^{3}$-defect–localized excitons coupled to a silicon photonic crystal cavity, representing one-dimensional host that provides telecom-band, room-temperature single-photon emission enhanced by cavity quantum electrodynamics. (c) Atom-like defect centres in hexagonal boron nitride (hBN), with (insets) an atomic model, confocal map and antibunching trace, illustrating a two-dimensional van der Waals host that supports room-temperature single-photon emission with transition energy tunable by strain and local environment. (d) Layer-poled thin-film lithium niobate (LN) waveguide supporting cascaded SHG and spontaneous parametric down-conversion (SPDC), highlighting a three-dimensional ferroelectric platform nanostructured and poled to generate bright photon pairs across multiple telecom bands on an integrated chip (refer to Table 1.1 for a quantitative comparison of operating temperature, radiative lifetime, and coherence time of quantum materials). Figure panels are adapted with permission from: (a) ref. Uppu2020SciAdv; (b) ref. Ishii2018NanoLett; (c) ref. Grosso2017NatCommun, (d) ref. Shi2024LPLN
• Figure 3: Milestones in hybrid and heterogeneous integration of solid-state quantum emitters (QEs) with low-loss QPIC platforms, highlighting routes to scalable, stable, and efficient cavity–emitter interaction systems. (a) Transfer printing (top) and direct CVD growth (bottom) of 2D materials (WSe$_2$, hBN) on SiN waveguides to realize localized quantum emitters coupled to guided modes; insets: flake–waveguide interface (top) and zoomed optical images of as-grown hBN emitters on the waveguide (bottom). (b) Wafer-bonded bulk emitters on PICs, with a single InAs QD in a GaAs nanowaveguide adiabatically coupled to a SiN chip (left) and NV centers in nanodiamonds coupled to photonic crystal cavities (right) insets: measured $g^{(2)}(0)$ under QD–cavity coupling (left) and cavity-enhanced NV emission (right). (c) Monolithic on-chip integration of hBN, serving as a host of defect-based extrinsic quantum emitters (top), and SiN, acting as a source of intrinsic quantum emitters (bottom), in simple nanophotonic waveguides, enabling generation and routing of single photons on the same platform; insets: PL spectra revealing multiple, spectrally distinct extrinsic and intrinsic emitter species respectively. (d) Pick-and-place integration of heterogeneous quantum microchiplets, with III–V QD sources aligned into prefabricated PIC sockets using micromanipulators; insets: quantum signature of triggered single-photon emission. (e) Deterministic creation of photostable vacancy-based emitters into AlN waveguides via He-ion implantation followed by thermal annealing; inset: confocal image with isolated emitters. (f) Photonic interconnects bridging external quantum emitters and photonic chips: externally generated high-quality quantum emitters interfaced with programmable SiN PICs (left panel, histograms showing qubit measurements) and a III–V QEs-based chip is photonic wire bonded to a SiN chip (right panel, SEM micrograph of the wire-bonded interface). Figure panels are adapted with permission from: (a) ref. Peyskens2019Glushkov2021; (b) ref. Davanco2017Schrinner2020; (c) ref. Senichev2022Li2021; (d) ref. Chanana2022ULLW; (e) ref. Lu2020; (f) ref. Wang2023Pfister2025.