Multipartite Quantum Clock Synchronization viaCollective Symmetric States

Abstract

This thesis investigates multipartite quantum clock synchronization (QCS) tasks using a class of quantum states, called collective symmetric (CS) states, which generalize Dicke and N00N states. Employment of CS states in previous QCS procedures is shown to improve synchronization performance in various network scenarios. The focus of the paper is on QCS procedures that, after the distribution of quantum states, rely exclusively on local operations and classical communication (LOCC), ensuring compatibility with highly noisy quantum channels. Two synchronization scenarios are considered: (i) synchronization between the two nodes of an arbitrarily chosen pair of nodes, and (ii) global synchronization where all nodes wish to synchronize their clocks to a common average time. First, a framework in which the previous procedures operate employing the CS states is introduced. Using such framework, possible limitations of the QCS procedures in terms of estimation ambiguity and lack of robustness are pointed out. Second, a procedure referred to as the tactical delay procedure (TDP) is proposed for each of the two synchronization scenarios. The TDP resolves the mentioned limitations and outperforms the state-of-the-art multi-partite QCS procedures in terms of synchronization precision without requiring additional quantum resources.