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arXiv:2505.09944 · Advanced Quantum Technologies

Advancements in Entangled Photon Pairs in 2D Van der Waal Materials for On‐Chip Quantum Device Applications

Abdus Salam Sarkar

Published Nov 23, 2025• 3 citations
arXivHTMLPDF

Abstract

ABSTRACT The next generation of technology is rooted in quantum‐based advancements. The entangled photon pair (EPP) sources play a pivotal role in such a wide range of advancements in quantum‐based device applications, including quantum‐ high‐precision sensors, communication, computing, cryptography, and so on. The bulk nonlinear crystals continue to dominate the current landscape of EPPs generation. However, emerging 2D quantum materials have demonstrated remarkable breakthroughs in both quantum photonics, nonlinear optics, and EPPs generation compared to conventional crystals. Their phase‐matching‐free spontaneous parametric down‐conversion (SPDC), ultrashort coherence length, lowest crystal symmetry, exceptionally large and anisotropic second‐order nonlinear susceptibility (), and seamless compatibility with on‐chip, silicon‐based photonic integration positions them as highly promising candidates for EPPs generation and next‐generation quantum photonic and quantum device technologies. This review article highlights recent breakthroughs and advancements in the generation of EPPs in 2D van der Waals (vdW) materials, with a focus on their applicability to quantum technologies and plausible on‐chip quantum integrated photonic device technology. The article begins by discussing the fundamental principles of EPPs generation. It provides a comprehensive review of the origin and generation of entangled photons in emerging layered vdW materials, alongside various optical quantum characterization techniques. The review then explores key physical parameters of the quantum states associated with EPPs. Additionally, it examines concepts related to the realization of paired photon generation at the quantum limit. The final section focuses on the potential for on‐chip integrated quantum device applications. Beyond highlighting recent advancements in quantum‐based research, the review also outlines the current limitations and future prospects aimed at advancing the field.

DOI
10.1002/qute.202500551

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ABSTRACT The next generation of technology is rooted in quantum‐based advancements. The entangled photon pair (EPP) sources play a pivotal role in such a wide range of advancements in quantum‐based device applications, including quantum‐ high‐precision sensors, communication, computing, cryptography, and so on. The bulk nonlinear crystals continue to dominate the current landscape of EPPs generation. However, emerging 2D quantum materials have demonstrated remarkable breakthroughs in both quantum photonics, nonlinear optics, and EPPs generation compared to conventional crystals. Their phase‐matching‐free spontaneous parametric down‐conversion (SPDC), ultrashort coherence length, lowest crystal symmetry, exceptionally large and anisotropic second‐order nonlinear susceptibility (), and seamless compatibility with on‐chip, silicon‐based photonic integration positions them as highly promising candidates for EPPs generation and next‐generation quantum photonic and quantum device technologies. This review article highlights recent breakthroughs and advancements in the generation of EPPs in 2D van der Waals (vdW) materials, with a focus on their applicability to quantum technologies and plausible on‐chip quantum integrated photonic device technology. The article begins by discussing the fundamental principles of EPPs generation. It provides a comprehensive review of the origin and generation of entangled photons in emerging layered vdW materials, alongside various optical quantum characterization techniques. The review then explores key physical parameters of the quantum states associated with EPPs. Additionally, it examines concepts related to the realization of paired photon generation at the quantum limit. The final section focuses on the potential for on‐chip integrated quantum device applications. Beyond highlighting recent advancements in quantum‐based research, the review also outlines the current limitations and future prospects aimed at advancing the field.
The realization of quantum light sources is crucial for advancing quantum technologies. Two‐dimensional van der Waals (vdW) materials offer a compelling platform for ultracompact entangled photon‐pair sources due to their strong optical nonlinearities and relaxed phase‐matching constraints. Here, the generation of entangled photon pairs from vdW NbOI 2 flakes on Au film via spontaneous parametric down‐conversion (SPDC) process is demonstrated. The observed inverse relationship between second‐order correlation function and pump power and the linear relationship between coincidence rate and pump power confirm the characteristic features of SPDC process. Furthermore, the measured polarization‐dependent coincidence rate shows the anisotropic entangled photon‐pair emission in NbOI 2 crystal. The dependence of coincidence rate on flake thickness is characterized by considering both optical interference and the phase‐matching effects. The demonstrated results open new avenues for the development of on‐chip integrated quantum photonic devices for applications in quantum state engineering, quantum communication, and quantum information processing.
Abstract Two-dimensional (2D) materials have been demonstrated as promising candidates for ultracompact entangled photon sources and on-chip integrated quantum photonic devices. Ferroelectric van der Waals materials have recently emerged as promising ultrathin sources of entangled photons via nonlinear optical processes. Here, the authors compare spontaneous parametric down conversion in NbOBr 2 and NbOI 2 , demonstrating near infrared polarization entangled photon generation and linking performance to crystal structure and optical properties. Our results extend the wavelength range of NbOX 2 -based SPDC sources and demonstrate NbOI 2 is especially suitable for near-infrared SPDC. Polarization entangled state (concurrence of 0.90 ± 0.05) can also be directly generated from NbOI 2 . Besides adding new candidates to the SPDC material library, our work provides new insight for the future generation of integrated quantum materials.
Abstract High-dimensional quantum entanglement is an important resource for emerging quantum technologies such as quantum communication and quantum computation. The scalability of metres-long experimental setups limits high-dimensional entanglement in bulk optics. Advancements in quantum technology hinge on reproducible, and reconfigurable quantum devices—including photon sources, which are challenging to achieve in a scalable manner using bulk optics. Advances in nanotechnology and CMOS-compatible integration techniques have enabled the generation of entangled photons on millimeter-scale chips, significantly enhancing scalability, stability, replicability, and miniaturization for real-world quantum applications. In recent years we have seen several chip-scale demonstrations with different discrete degrees of freedom including path, frequency-bin, time-bin, and transverse modes, on many material platforms. A complete quantum photonic integrated circuit requires the generation, manipulation, and detection of quantum states, involving various active and passive quantum photonic components which further increase the degree of complexity. Here, we focus on the high-dimensional versions of qubits—qudits—and review the nonlinear optical processes that facilitate on-chip high-dimensional entangled photon sources, and the currently used material platforms. We discuss a range of current implementations of on-chip high-dimensional entangled photon sources and demonstrated applications. We comment on the current challenges due to the limitations of individual material platforms and present future opportunities in hybrid and heterogeneous integration strategies for the next generation of integrated quantum photonic chips.
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Photon pairs generated by spontaneous parametric down-conversion (SPDC) are playing a pivotal role in many quantum applications such as quantum computing, quantum imaging and quantum communication. Metasurfaces, which are two-dimensional arrays of nanostructures, have been studied intensively to enhance SPDC and provide additional functionalities over the bulky optical systems [1]. Van der Waals (vdWs) layered materials have emerged as promising platform for quantum light sources, owing to their unique properties [2], [3]. For example, vdWs materials offer high refractive index, a high nonlinear susceptibility, and compatibility with on-chip integration.
ABSTRACT The recent emergence of van der Waals (vdW) materials with exceptional optical nonlinearity has driven advances in next‐generation nonlinear photonic devices beyond classical optics. While integrating these materials into fiber‐optic platforms offers unprecedented functionalities in quantum systems, realizing telecom‐band in‐line photon‐pair sources based on highly nonlinear vdW materials remains challenging. Here, we report photon‐pair generation centered at telecom wavelength via spontaneous parametric down‐conversion in a fiber‐integrated device incorporating a ferroelectric vdW crystal, SnP 2 S 6 . Benefiting from its giant optical nonlinearity and relaxed phase‐matching across near‐visible to telecom‐band wavelengths, a remarkable nonlinear conversion efficiency of 0.07% is achieved in a few‐micrometer‐thick SnP 2 S 6 film. Moreover, the fiber‐integrated SnP 2 S 6 device delivers high‐quality photon pairs at telecom wavelengths, achieving a detected coincidence rate of 102 counts/s. The coincidence‐to‐accidental ratio reached up to 55 662, which is much larger than that of previous vdW‐material‐based sources. Furthermore, the device generates polarization‐entangled photon pairs, which are verified via quantum state tomography to exhibit fidelities of 0.97 and concurrences of 0.95. This demonstration establishes a scalable, robust fiber‐integrated platform that combines the versatility of vdW materials, paving the way toward low‐loss, functionalized quantum photonic systems for networking, sensing, and computing.