Integrated photonics is emerging as a key technology for use in quantum information and communication. Driven by classical communication, which already has a swathe of scalable, efficient, and robust components, integrated photonics promises to transfer quantum science from a mere lab curiosity into a commercial reality. Chip-based quantum light sources are increasingly being recognized as a practical and high-performance alternative to bulky and power-hungry, table-top photon-pair sources. In particular, photon-pair sources based on spontaneous four-wave mixing in microring resonators (MRR) have emerged as a viable integrated photonic solution for quantum information and communication. This thesis relies on silicon nitride (Si3N4) MRR to realize narrowband, telecom photonpair sources. High quality factor MRRs are enabled by the low propagation losses in the Si3N4 platform; in this thesis, they are exploited to realize bright photon-pair sources with heralded spectral purity up to 0.98. Low quality factor MRRs are exploited for a proof-of-concept high-rate sequential time-bin entanglement with net visibilities up to 99.96 ± 0.03 %. For the goal of practical, real-world deployment of integrated photon-pair sources, it is not enough to demonstrate the performance of a single source. One also needs to demonstrate their high-performance operation in complex quantum networking protocols, such as entanglement swapping between genuinely independent sources. Here, for the first time, we demonstrate entanglement swapping between two independent, spatially separated, and asynchronously-pumped MRR photon-pair sources. Our sources operate in the continuous-wave regime, and time-resolved detection results in high Hong-Ou-Mandel (93.2 ±1.6 %) and entanglement swapping (91.2 ± 3.4 %) visibilities. Finally, to further improve our rates while maintaining high visibilities in multi-source interference scenarios, the origin of an on-chip-generated noise must be identified and mitigated. Here, we present our first efforts in the quest for tackling this notorious noise problem.
Integrated photonics is emerging as a key technology for use in quantum information and communication. Driven by classical communication, which already has a swathe of scalable, efficient, and robust components, integrated photonics promises to transfer quantum science from a mere lab curiosity into a commercial reality. Chip-based quantum light sources are increasingly being recognized as a practical and high-performance alternative to bulky and power-hungry, table-top photon-pair sources. In particular, photon-pair sources based on spontaneous four-wave mixing in microring resonators (MRR) have emerged as a viable integrated photonic solution for quantum information and communication. This thesis relies on silicon nitride (Si3N4) MRR to realize narrowband, telecom photonpair sources. High quality factor MRRs are enabled by the low propagation losses in the Si3N4 platform; in this thesis, they are exploited to realize bright photon-pair sources with heralded spectral purity up to 0.98. Low quality factor MRRs are exploited for a proof-of-concept high-rate sequential time-bin entanglement with net visibilities up to 99.96 ± 0.03 %. For the goal of practical, real-world deployment of integrated photon-pair sources, it is not enough to demonstrate the performance of a single source. One also needs to demonstrate their high-performance operation in complex quantum networking protocols, such as entanglement swapping between genuinely independent sources. Here, for the first time, we demonstrate entanglement swapping between two independent, spatially separated, and asynchronously-pumped MRR photon-pair sources. Our sources operate in the continuous-wave regime, and time-resolved detection results in high Hong-Ou-Mandel (93.2 ±1.6 %) and entanglement swapping (91.2 ± 3.4 %) visibilities. Finally, to further improve our rates while maintaining high visibilities in multi-source interference scenarios, the origin of an on-chip-generated noise must be identified and mitigated. Here, we present our first efforts in the quest for tackling this notorious noise problem.
Abstract Integrated photonics represents a technology that could greatly improve quantum communication networks in terms of cost, size, scaling, and robustness. A key benchmark for this is to demonstrate their performance in complex quantum networking protocols, such as entanglement swapping between truly independent photon-pair sources. Here, using two independent, asynchronously-pumped, integrated Si 3 N 4 microring resonator photon-pair sources, operating in the continuous-wave regime with time-resolved detections, we obtained state of the art Hong–Ou–Mandel (93.2 ± 1.6%) and entanglement swapping (91.2 ± 3.4%) visibilities, while maintaining high rates. The time-resolved detection facilitates high spectral purities without the need for spectral filtering. Our results demonstrate the potential of such telecom-band sources for practical, real-world quantum communication.
Abstract Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust, and scalable chip formats with applications in long-distance quantum-secured communication, quantum-accelerated information processing, and non-classical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers making them impractical, not reproducible prototype devices, hindering scalability and the transfer out of the lab into real-world applications. Here we demonstrate a fully integrated quantum light source, which overcomes these challenges through the combined integration of a laser cavity, a highly efficient tunable noise suppression filter (> 55 dB) exploiting the Vernier effect, and a nonlinear microring for entangled photon pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically-pumped InP gain section and a Si₃N₄ low-loss microring filter system and demonstrates high-performance parameters, i.e., a pair emission over four resonant modes in the telecom band (bandwidth ∼ 1 THz), and a remarkable pair detection rate of ∼ 620 Hz at a high coincidence-to-accidental ratio of ∼80. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), verified by quantum interference measurements with visibilities up to 96% (violating Bell-inequality) and by density matrix reconstruction through state tomography showing fidelities of up to 99%. Our approach, leveraging a hybrid photonic platform, enables commercial-viable, low-cost, compact, light-weight, and field-deployable entangled quantum sources, quintessential for practical, out-of-lab applications, e.g., in quantum processors and quantum satellite communications systems.
Compact, efficient, high-quality and scalable non-classical photon sources are one of the most critical building blocks for quantum information processing and communications. Photon pair generation via spontaneous four wave mixing is being recognized as an attractive platform for quantum optics which is compatible with the rapidly-maturing classical integrated photonics technology using silicon wafers, which is adopted in industry for its low cost, high performance and scalability. Traditionally, the photon pairs generated from silicon photonic devices, however, have not compared favorably with traditional nonlinear crystals in terms of overall rate, quality and efficiency. This dissertation discusses the factors that affect the quality and efficiency of photon pair generation in silicon integrated photonic microrings, together with their design and characterization. Furthermore, we show how the microrings can be integrated with other photonic devices on the silicon-on-insulator platform, and using proof-of-concept experiments, discuss the feasibility of using these photon-pair sources with technology that is already present in, or will soon be present in, practical fiber-optic networks, such as integrated lasers and modulated classical data streams.
With the rapid development of quantum information technology, fully connected multi-user quantum entanglement distribution networks have received increasing attention. Among these, multi-wavelength quantum light sources are key devices for establishing connections between multiple users. Despite recent impressive advances, there are still challenges in increasing the wavelength number of photon pairs due to limitations in the design and fabrication of nonlinear optical devices. The potentials of silicon nitride (Si3N4) microring resonators (MRRs), as scalable platforms for multi-wavelength quantum light sources, are explored in this work. The key design parameters of the Si3N4 MRRs, including waveguide dimension, resonator dispersion, and coupling condition, are comprehensively analyzed to optimize photon-pair generation. Based on these parameters, a Si3N4 MRR with a free spectral range of 20 GHz and an average quality factor of 1.6 million is designed and fabricated. This small free spectral range can generate more channels of correlated photon pairs by using the same wavelength resources. The high-quality resonator contributes to the enhancement of the rate of generating high photon pairs , which are critical for quantum entanglement distribution. With a continuous-wave pump laser, correlated photon pairs across a wide spectral range are generated through the spontaneous four-wave mixing (SFWM). The coincidence-to-accidental ratio (CAR) measurements verify the strong quantum correlation between photon pairs, highlighting the reliability of the system for entanglement distribution. Furthermore, the generation and output characteristics of quantum-correlated photon pairs are experimentally investigated with a tunable bandpass filter. The results demonstrate that 71 wavelength-correlated photon pairs within a 25.6 nm spectral range are successively generated as shown in the Fig. A. Our results pave the way for developing the multi-wavelength quantum light sources with Si3N4 platform, thereby advancing the multi-user quantum 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.
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.