Entangled photon-pair sources are essential components for emerging quantum information-processing technologies. Among various platforms, on-chip microresonators offer strong potential due to their resonant enhancement and suitability for wafer-scale integration. In this study, we demonstrate ultrabright entangled photon-pair generation from high- Q silicon microring resonators. By optimizing the device geometry and coupling configuration to suppress sidewall scattering and selectively excite the fundamental mode, we achieve single-mode resonance with an intrinsic Q -factor of 1.26 × 10 6 using only standard fabrication processes available in CMOS foundries. The resulting high- Q resonator yields a record-high brightness coefficient of 3.9 × 10 9 Hz/GHz/mW 2 . At an on-chip pump power of 240 μW, we obtain a maximum brightness of 22.0 MHz/GHz and a maximum photon-pair generation rate of 9.19 MHz. At a low-pump power of 10 μW, Franson-type two-photon interference exhibits a visibility of 98.0 ± 0.2%, confirming high-quality time–energy entanglement. These results show that narrow bandwidth and high generation rate can be achieved simultaneously in CMOS-compatible silicon photonic sources, thereby advancing their use in quantum repeaters and scalable quantum networks.
Entangled photon-pair sources are essential components for emerging quantum information-processing technologies. Among various platforms, on-chip microresonators offer strong potential due to their resonant enhancement and suitability for wafer-scale integration. In this study, we demonstrate ultrabright entangled photon-pair generation from high- Q silicon microring resonators. By optimizing the device geometry and coupling configuration to suppress sidewall scattering and selectively excite the fundamental mode, we achieve single-mode resonance with an intrinsic Q -factor of 1.26 × 10 6 using only standard fabrication processes available in CMOS foundries. The resulting high- Q resonator yields a record-high brightness coefficient of 3.9 × 10 9 Hz/GHz/mW 2 . At an on-chip pump power of 240 μW, we obtain a maximum brightness of 22.0 MHz/GHz and a maximum photon-pair generation rate of 9.19 MHz. At a low-pump power of 10 μW, Franson-type two-photon interference exhibits a visibility of 98.0 ± 0.2%, confirming high-quality time–energy entanglement. These results show that narrow bandwidth and high generation rate can be achieved simultaneously in CMOS-compatible silicon photonic sources, thereby advancing their use in quantum repeaters and scalable quantum networks.
Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip but the sources demonstrated so far require millimeter lengths and pump powers of the order of hundreds of mWs to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been demonstrated. Here we report the first demonstration of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell's inequality by as much as 11 standard deviations. The source is integrated on a silicon chip, operates at sub-mW pump power, emits in the telecom band with a pair generation rate exceeding 107 Hz per nm, and outputs into a photonic waveguide. These are all essential features of an entangled states emitter for a quantum photonic networks.
CMOS-compatible photonic chips are highly desirable for real-world quantum optics devices due to their scalability, robustness, and integration with electronics. Despite impressive advances using Silicon nanostructures, challenges remain in reducing their linear and nonlinear losses and in creating narrowband photons necessary for interfacing with quantum memories. Here we demonstrate the potential of the silicon nitride (Si3N4) platform by realizing an ultracompact, bright, entangled photon-pair source with selectable photon bandwidths down to 30 MHz, which is unprecedented for an integrated source. Leveraging Si3N4's moderate thermal expansion, simple temperature control of the chip enables precise wavelength stabilization and tunability without active control. Single-mode photon pairs at 1550 nm are generated at rates exceeding 107 s-1 with mW's of pump power and are used to produce time-bin entanglement. Moreover, Si3N4 allows for operation from the visible to the mid-IR, which make it highly promising for a wide range of integrated quantum photonics applications.
Photon-pair sources are critical building blocks for photonic quantum systems. Leveraging Kerr nonlinearity and cavity-enhanced spontaneous four-wave mixing, chip-scale photon-pair sources can be created using microresonators built on photonic integrated circuit. For practical applications, a high microresonator quality factor Q is mandatory to magnify photon-pair sources' brightness and reduce their linewidth. The former is proportional to Q^{4}, while the latter is inversely proportional to Q. Here, we demonstrate an integrated, microresonator-based, narrowband photon-pair source. The integrated microresonator, made of silicon nitride and fabricated using a standard CMOS foundry process, features ultralow loss down to 0.03 dB/cm and intrinsic Q factor exceeding 10^{7}. The photon-pair source has brightness of 1.17×10^{9} Hz/mW^{2}/GHz and linewidth of 25.9 MHz, both of which are record values for silicon-photonics-based quantum light source. It further enables a heralded single-photon source with heralded second-order correlation g_{h}^{(2)}(0)=0.0037(5), as well as an energy-time entanglement source with a raw visibility of 0.973(9). Our work evidences the global potential of ultralow-loss integrated photonics to create novel quantum light sources and circuits, catalyzing efficient, compact, and robust interfaces to quantum communication and networks.
Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip, but the devices demonstrated so far require millimeter lengths and pump powers of the order of hundreds of milliwatts to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been proven in these devices. Here we report the first demonstration, to the best of our knowledge, of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell’s inequality by more than seven standard deviations with an internal pair generation exceeding 107 Hz. The source is integrated on a silicon chip, operates at milliwatt and submilliwatt pump power, emits in the telecom band, and outputs into a photonic waveguide. These are all essential features of an entangled state emitter for a quantum photonic network.
Developing a high-quality, bright source of polarization-entangled photon pairs on CMOS-compatible integrated platforms, such as silicon or silicon nitride, remains a significant challenge. Here, a novel silicon chip-based nonlinear Sagnac interferometer, which mainly integrates a bidirectionally pumped microring resonator with a polarization-splitting rotator, was proposed to generate polarization-entangled photon pairs. By pumping the system with a pulsed laser at 1550 nm and a power of 78 μW, polarization-entangled photon pairs in the telecom C-band were produced through spontaneous four-wave mixing, achieving a state-of-the-art brightness of 1.6 × 107 pairs s−1 GHz−1 mW−2. Using an off-chip polarization analyzer, the visibility of polarization-correlation interference fringe was measured to be 96.6%. Quantum state tomography revealed a fidelity of 0.958 for the maximally entangled state produced by the source. These exceptional performance metrics, combined with the integrability of the device, make it highly suitable for advanced quantum applications, particularly in multi-user entanglement-based quantum communication networks.
High-dimensional entanglement provides valuable resources for quantum technologies, including quantum communication, quantum optical coherence tomography, and quantum computing. Obtaining a high brightness and dimensional entanglement source has significant value. Here we utilize a tunable asymmetric Mach–Zehnder interferometer coupled silicon microring resonator with 100 GHz free spectral range to achieve this goal. With the strategy of the tunable coupler, the dynamical and extensive tuning range of quality factors of the microring can be obtained, and then the biphoton pair generation rate can be optimized. By selecting and characterizing 28 pairs from a more than 30-pair modes biphoton frequency comb, we obtain a Schmidt number of at least 23.4 and on-chip pair generation rate of 19.9 MHz/mW2 under a low on-chip pump power, which corresponds to 547 dimensions Hilbert space in frequency freedom. These results will prompt the wide applications of quantum frequency comb and boost the further large density and scalable on-chip quantum information processing.