Chalcogenide glasses (ChGs) have recently emerged as enabling materials for building reconfigurable nanophotonic devices by employing their refractive index changes associated with photosensitive effects. In particular, the availability of low-loss thin-film ChGs and the realization of high-Q microresonators provide exciting opportunities for integrated photonics. So far, the ChG photonic devices are predominately operated in the classical optics regime. In this work, we present the realization on-chip bright photon-pair quantum light sources via spontaneous four-wave mixing in a high-Q microring resonator fabricated on the newly developed ChG Ge 25 Sb 10 S 65 platform. The emission wavelength of the photon-pair source can be continuously tuned across a double-free spectral range in a reconfigurable manner. Our work serves as a starting point to fully unleash the potential of exploiting ChGs for developing reconfigurable integrated quantum photonic devices.
Chalcogenide glasses (ChGs) have recently emerged as enabling materials for building reconfigurable nanophotonic devices by employing their refractive index changes associated with photosensitive effects. In particular, the availability of low-loss thin-film ChGs and the realization of high-Q microresonators provide exciting opportunities for integrated photonics. So far, the ChG photonic devices are predominately operated in the classical optics regime. In this work, we present the realization on-chip bright photon-pair quantum light sources via spontaneous four-wave mixing in a high-Q microring resonator fabricated on the newly developed ChG Ge 25 Sb 10 S 65 platform. The emission wavelength of the photon-pair source can be continuously tuned across a double-free spectral range in a reconfigurable manner. Our work serves as a starting point to fully unleash the potential of exploiting ChGs for developing reconfigurable integrated quantum photonic devices.
Being a key component on a photonic chip, the microring usually specializes in a certain nonlinear optical process and can not simultaneously meet different working conditions for different processes. Here, we theoretically and experimentally investigate a reconfigurable silicon microring resonator to act as a optimization strategy for both classical four-wave mixing and quantum light sources. Experimental results show that the four-wave mixing efficiency with continuous wave and pulsed pump can be both optimized to a high value well matching numerical analysis. A variety of quantum light sources - including the heralded single-photon source, two-photon source and multi-photon source - are demonstrated to present a high performance and their key parameters including the pair generation rates (PGR), the heralding efficiency (HE) and the coincidence-to-accidental ratio (CAR) are controllable and optimizable. Such tunable nonlinear converter is immune to fabrication variations and can be popularized to other nonlinear optical materials, providing a simple and compact post-fabrication trimming strategy for on-chip all-optical signal processing and photonic quantum technologies.
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.
Photonic integrated circuits (PICs) based on silicon-on-insulator (SOI) substrates provide a lightweight, compact platform for applications in quantum optics. We show the evaluation and characterization of an SOI-bascd PIC design for an entangled photon pair source, generating photon pairs by means of the nonlinear process of spontaneous four-wave mixing in microring resonators. Experimental results following from the chip fabrication fed back into the simulated parameter tuning effects, culminating in photon pair generation with measured correlations exceeding classically predicted limits.
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.
Single photons are the smallest indivisible quanta of light, canonically described by quantum mechanics. By carefully controlling the interaction of single photons, exquisite non-classical phenomena can be observed. Mature photonic chip technology has recently emerged as an ideal platform for quantum information processing using single photons. However, generating single photons efficiently on-chip remains a fundamental challenge. One solution is to harness the intrinsic nonlinearity available in certain photonic materials for nonlinear photon generation directly in on-chip waveguides themselves. This work examines nonlinear photon generation in two key material platforms. The first is chalcogenide glass. Chalcogenide, while highly nonlinear, is amorphous and thus has broadband Raman noise. In this study the Raman noise is characterised at the single-photon level to find an intrinsic minima, which is then targeted for low-noise photon generation using an engineered waveguide. The second platform is silicon. As silicon is complementary metal-oxide-semiconductor (CMOS) fabrication compatible, it is congruent with mass production. Thus, in this study, photon-pair generation is first shown in a compact photonic crystal, before combining two monolithic sources using active multiplexing. This thesis presents significant progress towards a key goal of the field – on- demand photon generation in a fully integrated photonic quantum processor.
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.