High-Brightness Bell Source Generation on a Thin-Film Lithium Niobate Integrated Circuit
Hansol Kim, Changhyun Kim, Minho Choi, Junhyung Lee, Yongchan Park, Sunghyun Moon, Jinil Lee, Hyeon Hwang, Min‐Kyo Seo, Y. -H. Kim, Y. -H. Kim, Hojoong Jung, Hyounghan Kwon
We demonstrate a compact, high-brightness polarization-entangled Bell state source on thin-film lithium niobate (TFLN), achieving 508.5 MHz/mW with high purity of 0.901, concurrence of 0.9, and fidelity of 0.944, enabling scalable quantum photonics.
Quantum photonics has rapidly advanced as a key area for developing quantum technologies by harnessing photons’ inherent quantum characteristics, particularly entanglement. Generation of entangled photon pairs, known as Bell states, is crucial for quantum communications, precision sensing, and quantum computing. While bulk quantum optical setups have provided foundational progress, integrated quantum photonic platforms now offer superior scalability, efficiency, and integrative potential. In this study, we demonstrate a compact and bright source of polarization-entangled Bell state utilizing continuous-wave pumping on thin film lithium niobate (TFLN) integrated photonics. Our periodically poled lithium niobate device achieves on-chip brightness of photon pair generation rate of 518.2 MHz/mW, comparable to representative integrated photon-pair sources reported across various integrated photonic platforms. This demonstration marks the first realization, to our knowledge, of polarization entanglement on TFLN platforms. Experimentally measured metrics confirm high-quality entangled photon pairs with a purity of 0.901, a concurrence of 0.9, and a fidelity of 0.941. We expect our compact quantum devices to have great potential for advancing quantum communication systems and photonic quantum technologies.
Quantum photonics has rapidly advanced as a key area for developing quantum technologies by harnessing photons' inherent quantum characteristics, particularly entanglement. Generation of entangled photon pairs, known as Bell states, is crucial for quantum communications, precision sensing, and quantum computing. While bulk quantum optical setups have provided foundational progress, integrated quantum photonic platforms now offer superior scalability, efficiency, and integrative potential. In this study, we demonstrate a compact and bright source of polarization-entangled Bell state utilizing continuous-wave pumping on thin film lithium niobate (TFLN) integrated photonics. Our periodically poled lithium niobate device achieves on-chip brightness of photon pair generation rate of 508.5 MHz/mW, surpassing other integrated platforms including silicon photonics. This demonstration marks the first realization of polarization entanglement on TFLN platforms. Experimentally measured metrics confirm high-quality entangled photon pairs with a purity of 0.901, a concurrence of 0.9, and a fidelity of 0.944. We expect our compact quantum devices to have great potential for advancing quantum communication systems and photonic quantum technologies.
Abstract Entanglement is central to quantum technologies such as cryptography, sensing, and computing. Photon pairs generated via nonlinear optical processes are excellent for preparing entangled states due to their long coherence times and compatibility with fiber optic networks. Steady progress in nanofabrication has positioned lithium niobate-on-insulator (LNOI) as a leading platform for monolithic integration of photon pair sources into optical circuits, leveraging its strong second-order nonlinearity. Here, we present a reconfigurable photonic integrated circuit on LNOI, which combines two on-chip photon pair sources with programmable interferometers, enabling the generation of entangled states. The photon pair sources achieve a source brightness of 26 MHz nm −1 mW −1 while maintaining a coincidence-to-accidental ratio above 100. We successfully interfere the two sources with 99.0 ± 0.7% visibility, demonstrating the indistinguishability required for producing entanglement on-chip. We show the preparation of any of the maximally entangled Bell states with fidelity above 90% verified by quantum state tomography. These results establish LNOI as a compelling, scalable platform to explore integrated quantum photonic technologies enabled by high-brightness sources of entangled quantum states.
Entangled photons are fundamental resources for quantum communication, computing, and networking. Among them, polarization-entangled photon pairs play an important role due to their straightforward state manipulation and direct use in quantum key distribution, teleportation, and network protocols. However, realizing compact, efficient, and scalable polarization-entangled sources that meet the requirements of practical deployment remains a major challenge. Here, we present a simple yet high-performance on-chip polarization-entangled photon-pair source on thin-film lithium niobate (TFLN). Our device employs dual quasi-phase matching (D-QPM) that sequentially supports type-0 and type-I spontaneous parametric down-conversion in a single nanophotonic waveguide, eliminating the need for interferometers, polarization rotators, or other complex circuits. The source directly produces high-fidelity Bell states with broad bandwidth, high brightness, and low noise. Using this integrated platform, we realize wavelength-multiplexed entanglement distribution in a four-user quantum network deployed over metropolitan fiber links up to 50 km. These results establish a robust and scalable pathway toward practical quantum communication systems and multi-user quantum mesh networks based on integrated photonics.
Abstract Scalable quantum networks require high-quality multi-wavelength light sources to enable simultaneous quantum communication among multiple users 1 . However, realizing such sources with high brightness, low noise, and chip-scale integration remains challenging. We demonstrate a high-quality and multi-wavelength quantum light source based on a periodically poled thin-film lithium niobate (TFLN) microring resonator employing spontaneous parametric down-conversion (SPDC) with a 100-GHz free spectral range (FSR), compatible with International Telecommunication Union (ITU) Channel Grid. In our experiment, twelve pairs of non-degenerate photon pairs are generated, exhibiting a photon-pair generation rate (PGR) of 817 MHz/mW, brightness of 1.86 × 10 9 Hz/mW 2 /GHz, and a coincidence-to-accidental ratio (CAR) of 51,829 ± 2204. The source enables predictable single photons with g (2) (0) = 0.015 ± 0.006 and energy-time entanglement with 99.5% raw visibility. Operating at room temperature, telecom wavelengths, and compatible with network channels, this work represents a crucial step toward realistic scalable, integrated quantum photonic networks in the future.