The combination of Quantum and Telecommunications networks, offering unparalleled quantum correlation-based capabilities and making it an ideal choice for certain critical applications, requires precise time synchronization across network nodes. This work analytically and experimentally assessed the application of the IEEE 1588 Precision Time Protocol in achieving time synchronization within quantum networks. As results, operating at a repetition rate of 5 MHz, the overall time synchronization precision is 65 ns for single-qubit detection and 100 ns for double-fold coincidence measurements. Correspondingly, the experimental results highlight the role of time-synchronization precision protocols in multi-node quantum networks and also provide insights for further developments for scalable quantum network infrastructure.
The combination of Quantum and Telecommunications networks, offering unparalleled quantum correlation-based capabilities and making it an ideal choice for certain critical applications, requires precise time synchronization across network nodes. This work analytically and experimentally assessed the application of the IEEE 1588 Precision Time Protocol in achieving time synchronization within quantum networks. As results, operating at a repetition rate of 5 MHz, the overall time synchronization precision is 65 ns for single-qubit detection and 100 ns for double-fold coincidence measurements. Correspondingly, the experimental results highlight the role of time-synchronization precision protocols in multi-node quantum networks and also provide insights for further developments for scalable quantum network infrastructure.
The combination of quantum and telecommunication networks enables to revolutionize the way information is used, offering unparalleled capabilities and making it an ideal choice for many critical applications. In this sense, quantum protocols generally have a unique requirement to have strict time synchronization in order to operate, which generally consume quantum resources of part of the exchanged qubits. Accordingly, work demonstrates and characterizes a temporal alignment mechanism for quantum networks based on frequency testing, allowing to preserve the quantum state of qubits. The time synchronization correction achieved is within 100 ns working at 5 MHz with temporal and relative frequency offsets commonly acquired in quantum links using conventional hardware clocks with temporal stability in the range of10−8and 200-ns jitter.
Quantum clock synchronization (QCS) aims to establish a shared temporal reference between distant nodes by exploiting uniquely quantum phenomena such as entanglement, single-photon interference, and quantum correlations. In contrast to classical synchronization and time-transfer techniques, which are limited by signal propagation delays, atmospheric disturbances, and oscillator drift, QCS protocols offer the potential to surpass classical precision bounds and enhance resilience against adversarial manipulations. As precise and secure time synchronization underpins distributed quantum networks, navigation systems, and emerging quantum Internet infrastructures, understanding QCS principles, capabilities, and implementation challenges has become increasingly important. This survey provides a unified and critical overview of the rapidly growing QCS research landscape, highlighting fundamentals, protocol types, enabling resources, performance constraints, security considerations, and practical implementations of QCS. We first introduce the theoretical underpinnings of QCS, including entanglement-assisted time transfer, Hong-Ou-Mandel interference-based synchronization, and quantum slow-clock transport. We then categorize the main QCS protocols, ranging from ticking-qubit and entanglement-based schemes to time-of-arrival correlation methods, conveyor-belt synchronization, and quantum-enhanced two-way time transfer. This organization clarifies the relationships between protocol families and their achievable precision advantages over classical methods. Key quantum resources such as spontaneous parametric down-conversion-based entangled photon pairs, Greenberger-Horne-Zeilinger and W multipartite states, squeezed and frequency-entangled light, quantum frequency combs, and quantum memories are reviewed in the context of scalability and robustness.
Time synchronization is crucial in the architecture of modern communication networks, supporting numerous high-stakes applications like financial transactions, autonomous vehicle control, and data center operations. While traditional time synchronization protocols, specifically the Network Time Protocol (NTP) and Precision Time Protocol (PTP), are reliable for various applications, they fall short in scenarios requiring ultra-high precision and resilience. To address these limitations, this paper provides a comprehensive comparative analysis of two emerging quantum technologies, namely Time-Correlated Entangled Photons (TCEP) and Optical Lattice Clocks (OLC). Using Monte Carlo simulations, we examined the synchronization in terms of the accuracy of these technologies under various noise conditions, revealing that while TCEP works perfectly in low-noise environments, its efficacy diminishes significantly with increasing noise levels. On the contrary, OLCs demonstrate consistent performance across various noise levels, making them more versatile for diverse application scenarios. This study is foundational for integrating quantum technologies in time synchronization for communication networks and sheds light on their merits and challenges. Our findings open new avenues for research in scalability, environmental resilience, and the development of hybrid quantum-classical timekeeping systems. Integrating quantum-enhanced time synchronization into a communication network will be the key step for achieving full-fledged Quantum Internet and quantum-enhanced communication networks.
Quantum Networking (QN) has the potential to revolutionize many areas of science and technology with the groundbreaking capabilities in communication and computation that it introduces. The quantum Internet is different from the classical Internet in that it is based on quantum bits (qubits), the fundamental units, rather than classical bits. This opens up the possibility of qubits being able to perform complex computation and communication tasks in ways that go beyond what is possible with classical systems because they can exist in multiple states at once through the principle of superposition. This is important for the future of quantum applications, in particular for satellite-based systems, to enable secure and efficient communication over long distances. However, there are still significant challenges to achieving scalable and reliable time synchronization and integration of quantum systems with existing classical networking infrastructures. This project focuses on these challenges. It will design, model, and experimentally evaluate a hardware clock system for integrating digital control boards in Quantum Networks, with an emphasis on scalable and reliable time synchronization architecture. It will model and benchmark time synchronization architectures using high-precision time measurement instruments and versatile microcontroller platforms. These microcontrollers mimic QN nodes and allow the experimentation of quantum communication protocols to evaluate how well the proposed solution can be scaled and performed. This work provides a foundation for addressing the technical issues of Quantum Networks. It is a step towards scalable quantum communication technologies and the development of future aerospace systems for secure global communication.
An important requirement in implementing distributed computing and sensing application is the synchronization of clocks at various locations. The Internet relies on the Network Time Protocol (NTP), which synchronizes clocks with accuracy in the order of milliseconds. More recently an ensemble of atomic clocks is used for navigation based on GPS. These clocks are highly accurate and provide time with very low uncertainty. Even so, many physics experiments such as distributed LIGO-based systems may require more accurate clock synchronization that is achievable using quantum entanglement. This requires the deployment of a network of quantum clocks synchronized by exploiting entangled atomic clock qubits. In this paper, we carry out a simulation study of synchronizing a network of quantum clocks interconnected by a fiber plant that supports the ESnet; the latter is used to support the classical communication needed for teleportation. We consider an existing protocol for synchro-nizing the atomic clock qubits that relies on the GHZ states. To assess the performance of the protocol we developed a discrete-event simulation of the network using IBM Qiskit framework for underlying quantum gate operations and measurements. The simulation results shed light on the resources required in terms of the number entangled qubits and the time needed to achieve the synchronization of different number of nodes in ESnet.
Time synchronization is a fundamental requirement in entanglement-based quantum networks, where the indistinguishability of photons in the time domain is essential for enabling Hong-Ou-Mandel interference and entanglement swapping. In addition to precise temporal alignment, it is equally crucial to ensure the stability of the reference clock over time, as even small fluctuations can degrade the overall performance of the network. In this work, we investigate the stability of clock synchronization for entanglement distribution based on entangled-photon sources operating in the telecommunication C-band. Temporal correlations between photon detection events are analyzed using time-tagged coincidence measurements, enabling the extraction of synchronization peaks and their long-term stability. Experimental results demonstrate that, once locked, the sources exhibit stable temporal correlations over an 8-hour acquisition period, with a maximum observed drift of approximately 120 ps, primarily associated with long fiber links. The width of the correlation peak remains consistent with detector jitter, indicating negligible additional system-induced temporal broadening. A central result of this work is the experimental synchronization between two entanglement-photon sources in a realistic metropolitan deployment, where entanglement distribution is performed over existing telecommunication infrastructure characterized by non-negligible losses and background noise. In this scenario, despite the presence of significant imperfections introduced by the metropolitan-scale fiber network, the observed correlations remain clearly detectable and are consistently well-approximated by Gaussian statistics. This confirms that the two sources can be reliably synchronized not only in controlled laboratory conditions but also under real-world operating constraints.