Single-photon Sources Unlock Secure Communication and Photonic Computing with Scalable Materials
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Single-photon emitters represent a crucial building block for next-generation technologies, promising breakthroughs in secure communication, photonic computing and the development of advanced network architectures.
Anuj Kumar Singh, Parul Sharma, and Kishor Kumar Mandal, all from the Indian Institute of Technology Bombay, alongside Lekshmi Eswaramoorthy and Anshuman Kumar, explore the rapidly evolving landscape of solid-state quantum light sources. Their work surveys the diverse materials now capable of generating bright, coherent single photons, ranging from atomic defects within crystals to excitonic states in nanoscale semiconductors. Importantly, this research highlights how recent advances in photonic integration allow for efficient control and manipulation of these emitters, paving the way for scalable photonic systems and potentially revolutionising fields like quantum computing and artificial intelligence. 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. Advances in photonic integration enable efficient routing, filtering, and on-chip manipulation of these emitters, paving the way for complex quantum systems. Strain-Engineered WSe2 Monolayer for Single Photons Scientists are developing solid-state single-photon emitters as essential resources for technologies including secure communication, photonic computing, and emerging network architectures. The research focuses on materials ranging from atom-like defects in crystals to excitonic states in low-dimensional semiconductors, aiming to create bright, coherent, and scalable sources of non-classical light. To achieve this, the team engineered a quantum key distribution (QKD) setup utilizing strain-engineered tungsten diselenide (WSe2) monolayers as single-photon sources. Pulsed lasers excite localized excitons within the monolayer, and their emission undergoes spectral filtering before coupling into a single-mode fiber. Polarization encoding of the BB84 states is achieved through fiber-based polarization control and a high-extinction polarizer, allowing encoded single-photon pulses to travel through a free-space or fiber link with variable attenuation simulating channel loss. Bob analyzes these pulses with a passive-basis polarization decoder consisting of non-polarizing and polarizing beam splitters, coupled with four single-photon detectors.
The team characterizes the non-classicality of the WSe2 source by measuring the second-order intensity autocorrelation, consistently demonstrating strong suppression of coincidences around zero delay, confirming dominantly single-photon emission. Furthermore, scientists developed a hybrid platform integrating deterministic single-photon emitters directly onto ultra-low-loss silicon nitride (Si3N4) circuits to address challenges in photonic quantum computing. This approach utilizes indium arsenide (InAs) quantum dots within gallium arsenide nanowaveguides placed onto buried Si3N4 waveguides, followed by an adiabatic mode transformer and a 50:50 multimode interference coupler. This setup enables triggered single-photon emission with a g(2)(0) value less than 0. 1, demonstrating a significant advancement in maintaining high flux of quality photons through increasingly complex circuits. The Si3N4 waveguides offer wafer-scale CMOS compatibility and propagation losses near 10−2 dB/m at telecom wavelengths, establishing a strong foundation for large quantum photonic processors. Single-Photon Sources Enable Photonic Quantum Computing Scientists have demonstrated a quantum photonic processor where integrated quantum dots exhibit strong antibunching, achieving a g(2)(0) value of approximately 0. 04, and clear evidence of coherent control, including a Mollow triplet and Rabi oscillations. These results, alongside previous demonstrations of waveguide-coupled resonance fluorescence and large-scale hybrid integration, point towards the creation of on-demand, nearly ideal single-photon sources injected into ultra-low-loss, reconfigurable networks with long delay lines and time-multiplexing stages. This combination fulfills the requirements for measurement-based photonic quantum computing, Gaussian boson sampling, and quantum repeater architectures, offering a practical path to scaling photonic quantum information processing on chip. Researchers also explored quantum-driven artificial intelligence using boson sampling, where N identical single photons traverse an M-mode linear-optical interferometer. Experiments reveal that this approach functions as a quantum random-feature model, improving classification accuracy on datasets as the number of optical modes increases. Notably, this boson-sampling reservoir outperforms a purely linear support-vector classifier using the same features and achieves performance comparable to an RBF-kernel SVM, but utilizes a physically generated feature map instead of a large random matrix.
The team confirmed that single-photon inputs significantly outperform coherent-state inputs in the same interferometer, demonstrating the importance of true many-boson interference for creating a larger and more expressive feature space. Investigations into materials for single-photon emitters reveal diverse platforms, each with unique trade-offs. Diamond, with nitrogen-vacancy (NV) centers, operates at room temperature with millisecond spin coherence, while silicon-vacancy (SiV) and germanium-vacancy (GeV) centers offer better optical linewidths at cryogenic temperatures. Silicon carbide, compatible with CMOS technology, also presents spin-active colour centres, and rare-earth doped crystals, like Y2SiO5:Er3+, exhibit long coherence times and optical transitions in the telecom band. Furthermore, two-dimensional materials, including WSe2, MoSe2, and WS2, host strain-localized excitonic quantum emitters, and hexagonal boron nitride demonstrates quantum emission at room temperature. Solid-State Single-Photon Emitters Integrated on Chip Researchers have made significant advances in the development of single-photon emitters, crucial components for emerging quantum technologies. These emitters, which produce individual particles of light, are now being realized in a diverse range of materials, spanning from zero-dimensional quantum dots to three-dimensional bulk crystals. This progress enables the creation of bright, coherent, and scalable sources of non-classical light, essential for applications like secure communication, photonic computing, and artificial intelligence. The integration of these solid-state emitters with photonic chips represents a key achievement, allowing for efficient routing, filtering, and manipulation of single photons on a small scale. This integration facilitates the creation of complex quantum circuits and networks, enabling photon-mediated coupling between spatially separated emitters and preserving quantum coherence over considerable distances. These advances underpin the potential for building practical quantum technologies, including quantum sensors, computers, and communication systems, and demonstrate the growing maturity of the field. Future research will likely focus on enhancing the performance of single-photon emitters, reducing losses in photonic circuits, and developing robust methods for controlling and manipulating quantum states. These efforts will be crucial for realizing the full potential of quantum technologies and translating them into real-world applications. 👉 More information 🗞 From Atomic Defects to Integrated Photonics: A Perspective on Solid-State Quantum Light Sources 🧠 ArXiv: https://arxiv.org/abs/2512.14402 Tags: