Quantum Key Distribution (QKD) leverages quantum effects to address the key distribution problem. Traditionally, its use has been limited to high-tech specialist networks for dedicated, trusted partners. However, advancements in hybrid quantum-classical networks now suggest the potential for QKD-level security on a wider scale.The Isabelle Infrastructure and Insider Framework (IIIf) has demonstrated the ability to formally verify security properties in proof-of-concept QKD models. In this paper, we build on these foundations to extend the formal analysis to real-world multi-photon QKD implementations. We enhance the existing model and show how IIIf’s attack tree analysis exposes threats such as the intercept-and-resend attack and the photon-number splitting (PNS) attack. Furthermore, refinement in IIIf enables the extraction of a formal specification for decoy-state QKD, strengthening security against vulnerabilities.

Abstract We present a programming language for describing and analysing concurrent quantum systems. We have an interpreter for programs in the language, using a symbolic rather than a numeric calculator, and we give its performance on examples from quantum communication and cryptography.

The novel field of quantum computation and quantum information has gathered significant momentum in the last few years. It has the potential to radically impact the future of information technology and influence the development of modern society. The construction of practical, general purpose quantum computers has been challenging, but quantum cryptographic and communication devices have been available in the commercial marketplace for several years. Quantum networks have been built in various cities around the world and a dedicated satellite has been launched by China to provide secure quantum communication. Such new technologies demand rigorous analysis and verification before they can be trusted in safety- and security-critical applications. Experience with classical hardware and software systems has shown the difficulty of achieving robust and reliable implementations. We present CCS q , a concurrent language for describing quantum systems, and develop verification techniques for checking equivalence between CCS q processes. CCS q has well-defined operational and superoperator semantics for protocols that are functional , in the sense of computing a deterministic input-output relation for all interleavings arising from concurrency in the system. We have implemented QEC (Quantum Equivalence Checker), a tool that takes the specification and implementation of quantum protocols, described in CCS q , and automatically checks their equivalence. QEC is the first fully automatic equivalence checking tool for concurrent quantum systems. For efficiency purposes, we restrict ourselves to Clifford operators in the stabilizer formalism, but we are able to verify protocols over all input states. We have specified and verified a collection of interesting and practical quantum protocols, ranging from quantum communication and quantum cryptography to quantum error correction.

No abstract available.

We define a language CQP (Communicating Quantum Processes) for modelling systems that combine quantum and classical communication and computation. CQP combines the communication primitives of the pi-calculus with primitives for measurement and transformation of the quantum state; in particular, quantum bits (qubits) can be transmitted from process to process along communication channels. CQP has a static type system, which classifies channels, distinguishes between quantum and classical data, and controls the use of quantum states. We formally define the syntax, operational semantics and type system of CQP, prove that the semantics preserves typing, and prove that typing guarantees that each qubit is owned by a unique process within a system. We also define a typechecking algorithm and prove that it is sound and complete with respect to the type system. We illustrate CQP by defining models of several quantum communication systems, and outline our plans for using CQP as the foundation for formal analysis and verification of combined quantum and classical systems.

We define a language CQP (Communicating Quantum Processes) for modelling systems which combine quantum and classical communication and computation. CQP combines the communication primitives of the pi-calculus with primitives for measurement and transformation of quantum state; in particular, quantum bits (qubits) can be transmitted from process to process along communication channels. CQP has a static type system which classifies channels, distinguishes between quantum and classical data, and controls the use of quantum state. We formally define the syntax, operational semantics and type system of CQP, prove that the semantics preserves typing, and prove that typing guarantees that each qubit is owned by a unique process within a system. We illustrate CQP by defining models of several quantum communication systems, and outline our plans for using CQP as the foundation for formal analysis and verification of combined quantum and classical systems.

In Shannon information theory, the capacity of a memoryless communication channel cannot be increased by the use of feedback from receiver to sender. In this correspondence, the use of classical feedback is shown to provide no increase in the unassisted classical capacity of a memoryless quantum channel when feedback is used across nonentangled input states, or when the channel is an entanglement-breaking channel. This gives a generalization of the Shannon theory for certain classes of feedback protocols when transmitting through noisy quantum communication channels.

In Shannon information theory the capacity of a memoryless communication channel cannot be increased by the use of feedback. The use of classical feedback is shown to provide no increase in the classical capacity of a memoryless quantum channel when feedback is used across nonentangled input states, or when the channel is an entanglement-breaking channel

Abstract. We compare two semantic models of dataflow programs: a synchronous version of the classical Kahn semantics, and a new semantics in a category of synchronous processes. We consider the Kahn semantics to be extensional, as it describes the functions computed by dataflow nodes, and the categorical semantics to be intensional, as it describes the step-by-step production of output tokens from input tokens. Assuming that programs satisfy Wadge’s cycle sum condition and are therefore deadlock-free, we prove that the two semantics are equivalent. This equivalence result amounts to a proof that function composition in the extensional semantics is faithfully modelled by the detailed interactions of the intensional semantics, and provides further insight into the nature of dataflow computation.

Proposes a typed calculus of synchronous processes based on the structure of interaction categories. Our aim has been to develop a calculus for concurrency that is canonical in the sense that the typed /spl lambda/-calculus is canonical for functional computation. We show strong connections between syntax, logic and semantics, analogous to the familiar correspondence between the typed /spl lambda/-calculus, intuitionistic logic and Cartesian closed categories.