This work models metropolitan-scale photonic quantum networks that use time bin encoding for quantum key distribution and quantum state teleportation. We develop and validate theoretical models by comparing them with prior experimental results. We use our newly developed simulator of quantum network communication, called SeQUeNCe, to perform simulations at the individual photon level with picosecond resolution. The simulator integrates accurate models of optical components including light sources, interferometers, detectors, beam splitters, and telecommunication fiber, allowing studies of their complex interactions. Optical quantum networks have been generating significant interest because of their ability to provide secure communication, enable new functionality such as clock synchronization with unprecedented accuracy, and reduce the communication complexity of certain distributed computing problems. In the past few years experimental demonstrations moved from table-top experiments to metropolitan-scale deployments and long-distance repeater network prototypes. As the number of optical components in these experiments increases, simulation tools such as SeQUeNCe will simplify experiment planning and accelerate designs of new network protocols. The modular design of our tool will also allow modeling future technologies such as network nodes with quantum memories and quantum transducers as they become available.
This work models metropolitan-scale photonic quantum networks that use time bin encoding for quantum key distribution and quantum state teleportation. We develop and validate theoretical models by comparing them with prior experimental results. We use our newly developed simulator of quantum network communication, called SeQUeNCe, to perform simulations at the individual photon level with picosecond resolution. The simulator integrates accurate models of optical components including light sources, interferometers, detectors, beam splitters, and telecommunication fiber, allowing studies of their complex interactions. Optical quantum networks have been generating significant interest because of their ability to provide secure communication, enable new functionality such as clock synchronization with unprecedented accuracy, and reduce the communication complexity of certain distributed computing problems. In the past few years experimental demonstrations moved from table-top experiments to metropolitan-scale deployments and long-distance repeater network prototypes. As the number of optical components in these experiments increases, simulation tools such as SeQUeNCe will simplify experiment planning and accelerate designs of new network protocols. The modular design of our tool will also allow modeling future technologies such as network nodes with quantum memories and quantum transducers as they become available.
Recent advances in quantum information science enabled the development of quantum communication network prototypes and created an opportunity to study full-stack quantum network architectures. This work develops SeQUeNCe, a comprehensive, customizable quantum network simulator. Our simulator consists of five modules: hardware models, entanglement management protocols, resource management, network management, and application. This framework is suitable for simulation of quantum network prototypes that capture the breadth of current and future hardware technologies and protocols. We implement a comprehensive suite of network protocols and demonstrate the use of SeQUeNCe by simulating a photonic quantum network with nine routers equipped with quantum memories. The simulation capabilities are illustrated in three use cases. We show the dependence of quantum network throughput on several key hardware parameters and study the impact of classical control message latency. We also investigate quantum memory usage efficiency in routers and demonstrate that redistributing memory according to anticipated load increases network capacity by 69.1% and throughput by 6.8%. We design SeQUeNCe to enable comparisons of alternative quantum network technologies, experiment planning, and validation and to aid with new protocol design. We are releasing SeQUeNCe as an open source tool and aim to generate community interest in extending it.
The nature-inspired field of quantum communication has witnessed exciting developments over the past few years with countries all over the world working hard to scale their experimental quantum networks to larger sizes and increased coverage. Evidently, quantum network simulators are the need of the hour as they provide a framework for tuning hardware parameters, optimizing control protocols, and testing configurations of large and complex quantum networks before their deployment in the real world. In this work, we present ShaNQar, Simulator of Network Quantique, a modular and customizable photonic quantum network simulator. It comprises models of components such as photons, lasers, neutral density filters, sources of entangled photon pairs, communication channels, mirrors, waveplates, beam splitters, single photon detectors, and nodes which incorporate a diverse set of tunable parameters for variability and versatility. It enables adaptive timing control and synchronization with virtually no simulation time resolution limit and features a plug-and-play design for faster coding and execution. We successfully simulated previous real-life experimental setups for quantum key distribution and quantum teleportation, thereby, demonstrating the reliability and accuracy of ShaNQar.
Efficient generation and high-quality distribution of entanglement is becoming increasingly more relevant in the field of quantum technologies, with important applications such as multiparty computation as well as quantum key distribution (QKD) on the rise. Quantum communication protocols based on entanglement offer an inherent quantum based randomness for key generation and provide in general higher security compared to prepare and measure implementations. Moreover, the future quantum internet will also be based on the distribution of entanglement for securely connecting quantum computers in a network.
In this work we show the feasibility of using sequential time-bin entangled states for quantum key distribution in metropolitan networks using off-the-shelf components. The time-bin encoding ensures high fidelity distribution robust against random polarisation fluctuations occuring in optical fibers. Modulated laser pulses in the GHz frequency range are used to generate time-bin entangled photon pairs. The entangled photons are then sent over an about 30km long (9.5dB loss) fiber link within the Vienna fiber network, showing high degree of distributed entanglement with a measured 93\% quantum visibility.
Quantum information technology has been developing rapidly in last two decades. Very recently, quite a few optical quantum key distribution networks have been reported, enabling preliminary practical applications in secure information transfer. Meanwhile, a number of significant progresses based on quantum network have also been made in the research of linear optical quantum computing, simulation and metrology. However, on the way towards large-scale optical quantum network serious problems occur. On the one hand, the distance of fiber-based quantum communication is limited, due to intrinsic fiber loss and decreasing of entanglement quality caused by the noisy environment. On the other hand, the probabilistic feature of single and entangled photon sources would also cause an exponentially increasing overhead for large-scale quantum network. To solve the above problems, quantum repeaters and/or transmission of optical quantum bits over free space channel can be efficiently exploited for future wide-area realization of quantum communication. In addition, memory built-in quantum repeaters would also enable scalable linear optical quantum computing, simulation and high precision measurement. In this talk I will present some recent experiments from our group, including eight-photon entanglement, topological quantum error-correction, quantum repeater and efficient and long-lived quantum memory, and entanglement distribution and quantum teleportation over 100km-scale free-space quantum channels. These experiments show the promising future possibility towards scalable quantum network with photons and atoms.
We extend the SeQUeNCe discrete-event simulator with physics-based models for polarization-encoded photonic quantum networks. Our framework integrates Jones-calculus optical components, including an SPDC Bell-state source, wave plates, and polarizing beam splitters, together with a multi-section fiber model capturing polarization mode dispersion, chromatic dispersion, and Raman noise from coexisting classical traffic. We validate the simulator by reproducing experimentally reported spectra, polarization correlations, quantum state tomography, and dispersion- and Raman-induced noise. The resulting platform enables hardware-parameterized prediction of entanglement distribution performance under realistic deployment conditions.
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.