Entanglement Verification in Quantum Networks with Tampered Nodes

In this paper, we consider the problem of entanglement verification across the quantum memories of any two nodes of a quantum network. Its solution can be a means for detecting (albeit not preventing) the presence of intruders that have taken full control of a node, either to make a denial-of-service attack or to reprogram the node. Looking for strategies that only require local operations and classical communication (LOCC), we propose two entanglement verification protocols characterized by increasing robustness and efficiency.Comment: 14 pages, 7 figure

Field test of quantum key distribution in the Tokyo QKD Network

A novel secure communication network with quantum key distribution in a metropolitan area is reported. Different QKD schemes are integrated to demonstrate secure TV conferencing over a distance of 45km, stable long-term operation, and application to secure mobile phones.Comment: 21 pages, 19 figure

The EPSRC Quantum Communications Hub

The Quantum Communications Hub is one of four Hubs comprising the research and development end of the UK National Quantum Technologies Programme. This programme is now in its second phase (2019-2024), following a successful first phase that ran 2014-2019. This Hub provides the UK focus for the quantum communications sector. This report provides a brief overview of the Hub's phase 1 developments, which mainly concentrated on progressing quantum key distribution (QKD) towards wider application. The grand vision of the phase 2 Hub is integrated secure quantum communications at all distance scales. For practicality and flexibility, this involves free-space communications at the shortest distance scales, fibre-based communications at the metropolitan and inter-city distance scales covered by current fibre networking, and free-space communications to support the very longest distances required for global reach. This report also outlines the ongoing Hub activities on short-range consumer QKD, fibre networking and long distance satellite-to-ground QKD. Brief discussion of the Hub work on new protocols, hybrid secure communications, standards and components is also given

A Reconfigurable Quantum Local Area Network Over Deployed Fiber

Practical quantum networking architectures are crucial for scaling the connection of quantum resources. Yet quantum network testbeds have thus far underutilized the full capabilities of modern lightwave communications, such as flexible-grid bandwidth allocation. In this work, we implement flex-grid entanglement distribution in a deployed network for the first time, connecting nodes in three distinct campus buildings time-synchronized via the Global Positioning System (GPS). We quantify the quality of the distributed polarization entanglement via log-negativity, which offers a generic metric of link performance in entangled bits per second. After demonstrating successful entanglement distribution for two allocations of our eight dynamically reconfigurable channels, we demonstrate remote state preparation -- the first realization on deployed fiber -- showcasing one possible quantum protocol enabled by the distributed entanglement network. Our results realize an advanced paradigm for managing entanglement resources in quantum networks of ever-increasing complexity and service demands

Deterministic And Efficient Three-party Quantum Key Distribution

The field of quantum computing is based on the laws of quantum mechanics, including states superposition and entanglement. Quantum cryptography is amongst the most surprising applications of quantum mechanics in quantum information processing. Remote state preparation allows a known state to a sender to be remotely prepared at a receiver’s location when they prior share entanglement and transmit one classical bit. A trusted authority in a network where every user is only authenticated to the third party distributes a secret key using quantum entanglement parity bit, controlled gates, ancillary states, and transmit one classical bit. We also show it is possible to distribute entanglement in a typical telecom metropolitan optical network

Connecting Quantum Cities: Simulation of a Satellite-Based Quantum Network

We present and analyse an architecture for a European-scale quantum network using satellite links to connect Quantum Cities, which are metropolitan quantum networks with minimal hardware requirements for the end users. Using NetSquid, a quantum network simulation tool based on discrete events, we assess and benchmark the performance of such a network linking distant locations in Europe in terms of quantum key distribution rates, considering realistic parameters for currently available or near-term technology. Our results highlight the key parameters and the limits of current satellite quantum communication links and can be used to assist the design of future missions. We also discuss the possibility of using high-altitude balloons as an alternative to satellites