Quantum networking enables the distribution of quantum information across distant nodes, unlocking capabilities such as secure communication, distributed quantum computing, enhanced metrology, and tests of fundamental physics. Photons serve as the natural carriers of quantum information over long distances due to their low loss in optical fibers and robustness to environmental decoherence. However, the practical realization of quantum networks remains limited by the lack of photon sources that are simultaneously compatible with diverse quantum systems, stable over long timescales, and suitable for deployment in real-world fiber infrastructure. This dissertation addresses these challenges through the co-development of photon-pair sources and a field-deployed quantum networking testbed. We present two complementary chip-scale sources of correlated photon pairs tailored for distinct bottlenecks in quantum networking. The first is a hybrid visible–telecom photon-pair source designed to address a fundamental spectral mismatch between quantum nodes and communication channels. While most quantum memories and processors operate at visible to near- nfrared wavelengths, optical fibers exhibit minimal loss in the telecommunications band. By integrating periodically poled nonlinear waveguides with photonic integrated circuits, we demonstrate a platform capable of directly generating visible–telecom photon pairs, enabling efficient interfacing between heterogeneous quantum systems and existing fiber networks. The second source is a fully packaged, broadband telecom photon-pair source based on silicon waveguide spirals, designed for stable, long-duration operation. This stability enables extended measurements necessary to overcome channel losses and environmental drifts in deployed fiber networks. These sources are evaluated within RoQNET (Rochester Quantum Network), a ∼20 km fiber link between the Rochester Institute of Technology and the University of Rochester. Using this platform, we demonstrate the transmission and on-chip modulation of heralded telecom single photons, verify their nonclassical statistics, and characterize long-term channel behavior. Additionally, we explore programmable time-bin entanglement distribution using spectral waveshapers, providing a flexible approach to quantum communication. Together, this work establishes a co-designed source–network framework for scalable, heterogeneous quantum networking.
Quantum networking enables the distribution of quantum information across distant nodes, unlocking capabilities such as secure communication, distributed quantum computing, enhanced metrology, and tests of fundamental physics. Photons serve as the natural carriers of quantum information over long distances due to their low loss in optical fibers and robustness to environmental decoherence. However, the practical realization of quantum networks remains limited by the lack of photon sources that are simultaneously compatible with diverse quantum systems, stable over long timescales, and suitable for deployment in real-world fiber infrastructure. This dissertation addresses these challenges through the co-development of photon-pair sources and a field-deployed quantum networking testbed. We present two complementary chip-scale sources of correlated photon pairs tailored for distinct bottlenecks in quantum networking. The first is a hybrid visible–telecom photon-pair source designed to address a fundamental spectral mismatch between quantum nodes and communication channels. While most quantum memories and processors operate at visible to near- nfrared wavelengths, optical fibers exhibit minimal loss in the telecommunications band. By integrating periodically poled nonlinear waveguides with photonic integrated circuits, we demonstrate a platform capable of directly generating visible–telecom photon pairs, enabling efficient interfacing between heterogeneous quantum systems and existing fiber networks. The second source is a fully packaged, broadband telecom photon-pair source based on silicon waveguide spirals, designed for stable, long-duration operation. This stability enables extended measurements necessary to overcome channel losses and environmental drifts in deployed fiber networks. These sources are evaluated within RoQNET (Rochester Quantum Network), a ∼20 km fiber link between the Rochester Institute of Technology and the University of Rochester. Using this platform, we demonstrate the transmission and on-chip modulation of heralded telecom single photons, verify their nonclassical statistics, and characterize long-term channel behavior. Additionally, we explore programmable time-bin entanglement distribution using spectral waveshapers, providing a flexible approach to quantum communication. Together, this work establishes a co-designed source–network framework for scalable, heterogeneous quantum networking.
Quantum communication promises unconditional security by leveraging the fundamental laws of quantum physics, which make eavesdropping detectable through the disturbance it introduces in quantum states. A cornerstone of this technology is quantum key distribution (QKD), enabling the distribution of a shared secret key between distant users with information- theoretic security, rather than relying on assumptions about an eavesdropper’s computational power, as in classical cryptography. However, current QKD systems rely largely on bulk-optical solutions, which limits scalability, stability, and integration into existing telecommunication infrastructures. Photonic integrated circuits (PICs) offer a promising platform to overcome these challenges by providing compact, stable, and CMOS-compatible architectures. This PhD work investigates integrated photonic platforms for practical quantum communication at telecommunication wavelengths, with a focus on demonstrating QKD protocols across three different encoding schemes: time-bin, frequency-bin, and path. First, a time-bin QKD receiver using a borosilicate-glass integrated imbalanced Mach–Zehnder interferometer (iMZI) is developed and compared with a fiber-based receiver, showing enhanced phase stability and improved long-distance secure key rates. Next, frequency-bin entanglement-based QKD is implemented using silicon microring resonators, demonstrating high-visibility quantum interference and active phase-stabilization techniques. Finally, a chip-to-chip path-entangled QKD link is realized using silicon photonic spiral sources, representing a crucial step toward fully integrated quantum transceivers. Across these experiments, this PhD thesis establishes a unified experimental framework for integrated QKD and evaluates performance in terms of quantum bit error rate, secure key rate, and system stability under realistic operating conditions. Together, the results provide a proof-of-concept demonstration of scalable, high-performance quantum communication using PIC technology, advancing toward practical deployment in future quantum networks and laying foundations for multidimensional and fully integrated quantum communication nodes.
Photon pair sources are fundamental building blocks for quantum entanglement and quantum communication. Recent studies in silicon photonics have documented promising characteristics for photon pair sources within the telecommunications band, including sub-milliwatt optical pump power, high spectral brightness, and high photon purity. However, most quantum systems suitable for local operation (e.g., storage/computation) support optical transitions in the visible or short nearinfrared bands. In comparison to telecommunications wavelengths, the significantly higher optical attenuation in silica at such wavelengths limits the length scale over which optical-fiber-based quantum communication between such local nodes can take place. One approach to connect such systems over fiber is through a photon pair source that can bridge the visible and telecom bands, but an appropriate source, which should produce narrow-band photon pairs with a high signal-to-noise ratio, has not yet been developed in an integrated platform. Here, we demonstrate a nanophotonic visible-telecom photon pair source for the first time, using high quality factor silicon nitride resonators to generate narrow-band photon pairs with unprecedented purity and brightness, with coincidence-toaccidental ratio (CAR) up to 3,780 ± 140 and detected photon-pair flux up to (18,400 ± 1,000) pairs/s. We further demonstrate visible-telecom time-energy entanglement and its distribution over a 20 km fiber, far exceeding the fiber length over which purely visible wavelength quantum light sources can be transmitted. Finally, we show how dispersion engineering of the microresonators enables the connections of different species of trapped atoms/ions, defect centers, and quantum dots to the telecommunications bands for future quantum communication systems.
Photonic links between disparate quantum technologies−such as photon sources, memories, processors, clocks, and sensors−are key to scaling quantum networks and realizing a versatile quantum internet for secure quantum communication, distributed quantum computing, and entanglement-enhanced metrology. In practice, each technology is most suitably implemented on a different quantum platform; the substantial spectral mismatch between them, along with scarce native telecom interfaces, thus poses a major bottleneck to achieving efficient interconnections over long distances. Here we demonstrate the first deployed two-node hybrid network that operates entirely in the telecom C-band. Our approach uses no quantum frequency conversion or external filtering; instead, we develop a neutral atom single photon source and a solid-state rare-earth quantum memory that both operate in previously unexplored telecom regimes with state-of-the-art performance. The source achieves a high single-photon purity at 46 kcps, and the memory a storage efficiency of 10.6% with high multimode capacity. We leverage the intrinsic tunability of both systems to optimize their spectral overlap and demonstrate microsecond-level storage and retrieval with a large time-bandwidth product. Moreover, we showcase real-world networking competencies such as support for multiplexing across 37 temporal modes and preservation of non-classicality over fibers of 10.6 km (metropolitan) and 49.2 km (laboratory). Our work establishes a backbone for telecom-native quantum repeater links and unlocks a path towards high-bandwidth, large-scale quantum networking.
Quantum networks exhibit enhanced performance compared to their classical counterparts, enabling secure communication and enhanced sensing protocols. Scalable quantum networks must transmit photons over distances ranging from kilometers to metropolitan scales while preserving entanglement. The objective of this thesis is to characterize the sources and switches of real-world deployed quantum networks, which require an intimate knowledge of nonlinear concepts and devices that drive these operating regimes. Importantly, quantum networks are deployed alongside existing classical communication infrastructure to ensure scalability and compatibility with established fiber-based systems. As a result, quantum and classical signals must coexist within the same telecommunication network. Because quantum infrastructure relies on optical fiber, these networks are susceptible to instabilities arising from fiber- induced effects. To fully realize a scalable quantum network, we investigated the quantum physical layer to optimize performance and identify limitations in our networking system. We characterized the performance of an entangled-photon source used to produce polarization-entangled photons. We then observe how well a high-speed, low-loss quantum switch preserves entanglement, demonstrating its utility for transmitting photons to different nodes in scalable quantum networks. We then analyze a 30 km deployed fiber located in the DC metropolitan area to examine how fiber-induced effects influence network performance. Quantum networks uniquely leverage quantum phenomena to enable fundamentally secure communication and distributed quantum computing beyond the capabilities of classical systems. To realize these advantages, careful characterization of the quantum physical layer and deployed fiber-based networks is essential, as it ensures the stability, reliability, and high-fidelity operation required for large-scale quantum network applications.
Quantum networks based on wavelength-multiplexed entanglement enable parallel distribution of quantum correlations, increasing channel capacity for secure communication and distributed quantum information processing. However, broadband integrated sources capable of generating multipartite entanglement beyond photon pairs remain scarce. Here we report on-chip generation of telecom-band four-photon entanglement in a periodically poled thin-film lithium niobate on insulator (LNOI) waveguide. Type-0 spontaneous parametric down-conversion provides a phase-matching bandwidth exceeding 200 nm, enabling spectrally separable generation of multi-photon entanglement across the telecom band. The generated photons are encoded in time bins for robust fiber compatibility, and a coherent interface enabling reversible conversion between time-bin and polarization degrees of freedom allows complete quantum state tomography. We measure two-photon entanglement with a brightness of 6.7 MHz/mW/nm and a fidelity of 0.874±0.002. At a pump power of 0.08 mW, the four-photon state exhibits a fourfold coincidence rate of 1 Hz and a fidelity of 0.74±0.01, representing a threefold improvement over previous integrated platforms. Our results establish LNOI as a scalable platform for broadband multi-photon entanglement and provide a practical route toward dense wavelength-multiplexed quantum networks.
The ability to control the optical frequency of quantum state carriers (i.e. photons) is an important functionality for future quantum networks. It allows all matter quantum systems - nodes of the network - to be compatible with the telecommunication C-band, therefore enabling long distance fiber quantum communication between them. It also allows dissimilar nodes to be connected with each other, thus resulting in heterogeneous networks that can take advantage of the different capabilities offered by the diversity of its constituents. Quantum memories are one of the building blocks of a quantum network, enabling the storage of quantum states of light and the entanglement distribution over long distances. In our group, two different types of memories are investigated: a cold atomic ensemble and an ion-doped crystal. In this thesis I investigate the quantum frequency conversion of narrow-band photons, emitted or absorbed by optical quantum memories, with two different objectives: the first one is to connect quantum memories emitting or absorbing visible single photons with the telecommunication wavelengths, where fiber transmission loss is minimum. The second and main goal is to study the compatibility between disparate quantum nodes, emitting or absorbing photons at different wavelengths. More precisely the objective is to achieve a quantum connection between the two optical memories studied using quantum frequency conversion techniques. The main core of this work is the quantum frequency conversion interface that bridges the gap between the cold ensemble of Rubidium atoms, emitting photons at 780nm, and the Praseodymium ion doped crystal, absorbing photons at 606nm. This interface is composed of two different frequency conversion devices, where a cascaded conversions takes place: the first one converts 780nm photons to the telecommunication C-band, and the second one converts them back to visible, at 606nm. This comes with several challenges such as conversion efficiency, phase stability and parasitic noise reduction, which are important considerations to show the conservation of quantum behaviors through the conversion process. This work can be divided in three parts. In a first one, we built a quantum frequency conversion interface between 606nm and the C-band wavelength, capable of both up and down-conversion of single photon level light. We also characterized the noise processes involved in this specific conversion. In the down-conversion case we showed that memory compatible heralded single photons emitted from a photon pair source preserve their non-classical properties through the conversion process. In the up-conversion case, we showed the storage of converted telecom photons in the praseodymium doped crystal, and their retrieval with high signal to noise ratio. The second part of the work was devoted to the conversion of photons from an emissive Rubidium atomic quantum memory to the telecom C band. In this work we converted the heralding photons from the atomic ensemble and measured non-classical correlations between a stored excitation and a C-band photon, necessary for quantum repeater applications. In the last part of the thesis, we setup the full frequency conversion interface and showed that heralded photons emitted by the atomic ensemble are converted, stored in the solid state memory and retrieved with high signal to noise ratio. We demonstrated that a single collective excitation stored in the atomic ensemble is transfered to the crystal by mean of a single photon at telecom wavelength. We also showed time-bin qubit transfer between the two quantum memories. This work represents the first proof of principle of a photonic quantum connection between disparate quantum memory nodes. The results presented in this thesis pave the way towards the realization of modular and hybrid quantum networks.