Abstract This paper investigates multipartite quantum clock synchronization (QCS) procedures using a new class of quantum states called collective symmetric (CS) states, which generalize Dicke and N00N-type states. Among all the QCS techniques proposed in the literature, the focus here is on procedures relying on local operations and classical communication (LOCC). Two synchronization scenarios that are particularly useful for quantum networks are considered: (i) pair synchronization where multiple arbitrarily chosen disjoint pairs of nodes aim to align their clocks, and (ii) network synchronization where all nodes aim to synchronize their clocks to a common average time. First, the paper discusses the use of CS states in QCS procedures previously proposed in the literature for both scenarios. Second, possible limitations of the QCS procedures are considered in terms of insufficient robustness and estimation ambiguity. Third, a new procedure, referred to as efficient synchronization procedure (ESP), is designed for each of the two synchronization scenarios. The ESP is shown to address the aforementioned limitations and to outperform the state-of-the-art LOCC-based multipartite QCS procedures in terms of synchronization precision.
Abstract This paper investigates multipartite quantum clock synchronization (QCS) procedures using a new class of quantum states called collective symmetric (CS) states, which generalize Dicke and N00N-type states. Among all the QCS techniques proposed in the literature, the focus here is on procedures relying on local operations and classical communication (LOCC). Two synchronization scenarios that are particularly useful for quantum networks are considered: (i) pair synchronization where multiple arbitrarily chosen disjoint pairs of nodes aim to align their clocks, and (ii) network synchronization where all nodes aim to synchronize their clocks to a common average time. First, the paper discusses the use of CS states in QCS procedures previously proposed in the literature for both scenarios. Second, possible limitations of the QCS procedures are considered in terms of insufficient robustness and estimation ambiguity. Third, a new procedure, referred to as efficient synchronization procedure (ESP), is designed for each of the two synchronization scenarios. The ESP is shown to address the aforementioned limitations and to outperform the state-of-the-art LOCC-based multipartite QCS procedures in terms of synchronization precision.
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.
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. Practical limitations arising from decoherence, channel loss, dispersion, detector timing jitter, and relativistic effects are examined alongside emerging noise mitigation strategies. Security aspects—including eavesdropping on time correlations, intercept-resend attacks, and adversarial delay manipulation—are evaluated with respect to trusted and untrusted network architectures. Recent proof-of-concept demonstrations in fiber networks, free-space optical links, chip-integrated photonic systems, and satellite-ground platforms are summarized, followed by discussions of open challenges toward precise and secure global quantum-synchronized networks.
We propose a multiparty quantum clock synchronization protocol that makes optimal use of the maximal multipartite entanglement of GHZ-type states. To realize the protocol, different versions of maximally entangled eigenstates of collective energy are generated by local transformations that distinguish among different groupings of the parties. The maximal sensitivity of the entangled states to time differences between the local clocks can then be accessed if all parties share the results of their local time-dependent measurements. The efficiency of the protocol is evaluated in terms of the statistical errors in the estimation of time differences and the performance of the protocol is compared to alternative protocols proposed previously.
Recently a protocol for Quantum Clock Synchronization (QCS) of remote clocks using quantum entanglement was proposed by Jozsa et al. This method has the goal of eliminating the random noise present in classical synchronization techniques. However, as stated QCS depends on the two members of each entangled pair undergoing the same unitary evolution even while being transported to different locations. This is essentially equivalent to a perfect Eddington Slow Clock Transfer protocol and thus, not an improvement over classical techniques. We will discuss this and suggest ways in which QCS may still be used.
The ability to measure, hold and distribute time with high precision and accuracy is a foundational capability for scientific exploration. Beyond fundamental science, time synchronization is an indispensable feature of public and private communication, navigation and ranging, and distributed sensing, amongst others technological applications. We propose the implementation of a quantum network of satellite- and ground-based clocks with the ability to implement Quantum Clock Synchronization to picosecond accuracy. Implementation of the proposed QCS network offers a double advantage: (1) a more accurate, robust, and secure time synchronization network for classical applications than currently possible, and (2) a resource to fulfill the much more stringent synchronization requirements of future quantum communication networks.
The quantum clock synchronization (QCS) is to measure the time difference among the spatially separated clocks with the principle of quantum mechanics. The first QCS algorithm proposed by Chuang and Jozsa is merely based on two parties, which is further extended and generalized to the multiparty situation by Krco and Paul. They present a multiparty QCS protocol based upon W states that utilizes shared prior entanglement and broadcast of classical information to synchronize spatially separated clocks. Shortly afterwards, Ben-Av and Exman came up with an optimized multiparty QCS using Z state. In this work, we firstly report an implementation of Krco and Ben-AV multiparty QCS algorithm using a four-qubit Nuclear Magnetic Resonance (NMR). The experimental results show a great agreement with the theory and also prove Ben-AV multiparty QCS algorithm more accurate than Krco.