Biblio

Can quantum entanglement increase the capacity of (classical) covert channels? To one familiar with Holevo's Theorem it is tempting to think that the answer is obviously no. However, in this work we show: quantum entanglement can in fact increase the capacity of a classical covert channel, in the presence of an active adversary; on the other hand, a zero-capacity channel is not improved by entanglement, so entanglement cannot create ‘purely quantum’ covert channels; the problem of determining the capacity of a given channel in the presence of entanglement is undecidable; but there is an algorithm to bound the entangled capacity of a channel from above, adapted from the semi-definite hierarchy from the theory of non-local games, whose close connection to channel capacity is at the core of all of our results.

Quantum entanglement gives rise to a range of non-classical effects, which are extensively exploited in quantum computing and quantum communication. Therefore, detection and quantification of entanglement as well as preparation of highly entangled quantum states remain the fundamental objectives in these fields. Much attention has been devoted to the studies of graph states, which play a role of a central resource in quantum error correction, quantum cryptography and practical quantum metrology in the presence of noise.We examine multi-qubit graph states generated by the action of controlled phase shift operators on a separable quantum state of a system, in which all the qubits are in arbitrary identical states. Analytical expression is obtained for the geometric measure of entanglement of a qubit with other qubits in graph states represented by arbitrary graphs. We conclude that this quantity depends on the degree of the vertex corresponding to the qubit, the absolute values of the parameter of the phase shift gate and the parameter of the initial state the gate is acting on. Moreover, the geometric measure of entanglement of certain types of graph states is quantified on the IBM’s quantum computer ibmq\_athens based on the measurements of the mean spin. Namely, we consider states associated with the native connectivity of ibmq\_athens, the claw and the complete graphs. Appropriate protocols are proposed to prepare these states on the quantum computer. The results of quantum computations verify our theoretical findings [1].

We study quantum-secure covert-communication over lossy thermal-noise bosonic channels, the quantum mechanical model for many practical channels. We derive the expressions for the covert capacity of these channels: Lno-EA, when Alice and Bob share only a classical secret, and LEA, when they benefit from entanglement assistance. Entanglement assistance alters the fundamental scaling law for covert communication. Instead of Lno-EA$\surd$n-rno-EA(n), rno-EA(n) = o($\surd$n), entanglement assistance allows LEA$\surd$n log n - rEA(n), rEA(n) = o($\surd$n log n), covert bits to be transmitted reliably over n channel uses. However, noise in entanglement storage erases the log n gain from our achievability; work on the matching converse is ongoing.

The design of large-scale quantum networks and any future quantum internet will rely on quantum repeaters and how quantum information flows through it. Tasks performed on such networks will go well beyond quantum key distribution and are likely to include quantum remote sensing and distributed quantum computation. In this presentation we will explore the various ways that such networks could be designed to support those advanced tasks. Critical to this will be quantum routing which we should is highly dependent on the repeater architecture. We introduce a quantum quality of service to help characterize the systems performance and shows how it leads interesting network and routing behavior.

We propose a multipartite quantum communication network (QCN) based on surface codes (SCs). We describe how simultaneously to entangle multiple nodes in an arbitrary network topology by employing the SCs. We further describe how to extend the transmission distance between arbitrary two nodes by using the SCs as well. Finally, we describe how to operate the proposed QCN by employing the SDN concept.

When using digital signatures, we need to deal with the problem of fairness of information exchange. To solve this problem, Chen, etc. introduced a new conception which is named concurrent signatures in Eurocrypt'04. Using concurrent signatures scheme, two entities in the scheme can generate two ambiguous signatures until one of the entities releases additional information which is called keystone. After the keystone is released, the two ambiguous signatures will be bound to their real signers at the same time. In order to provide a method to solve the fairness problem of quantum digital signatures, we propose a new quantum concurrent signature scheme. The scheme we proposed does not use a trusted third party in a quantum computing environment, and has such advantages as no need to conduct complex quantum operations and easy to implement by a quantum circuit. Quantum concurrent signature improves the theory of quantum cryptography, and it also provides broad prospects for the specific applications of quantum cryptography.

This article shows the analogy between natural language texts and quantum-like systems on the example of the Bell test calculating. The applicability of the well-known Bell test for texts in Russian is investigated. The possibility of using this test for the text separation on the topics corresponding to the user query in information retrieval system is shown.

A new quantum secret sharing protocol based on the ping-pong protocol of quantum secure direct communication is proposed. The pairs of entangled qutrits are used in protocol, which allows an increase in the information capacity compared with protocols based on entangled qubits. The detection of channel eavesdropping used in the protocol is being implemented in random moments of time, thereby it is possible do not use the significant amount of quantum memory. The security of the proposed protocol to attacks is considered. A method for additional amplification of the security to an eavesdropping attack in communication channels for the developed protocol is proposed.

We discuss the current landscape in quantum communication and cryptography, and focus in particular on recent photonic implementations, using encoding in discrete or continuous properties of light, of central quantum network protocols, enabling secret key distribution, verification of entangled resources and transactions of quantum money, with maximal security guarantees. We also describe current challenges in this field and our efforts towards the miniaturization of the developed photonic systems, their integration into telecommunication network infrastructures, including with satellite links, as well as the practical demonstration of novel protocols featuring a quantum advantage in communication efficiency for a wide range of useful tasks in a network environment. These advances enrich the resources and applications of the emerging quantum networks that will play a central role in the context of future quantum-safe communications.

We report a an experimental study of device-independent quantum random number generation based on an detection-loophole free Bell test with entangled photons. After considering statistical fluctuations and applying an 80 Gb × 45.6 Mb Toeplitz matrix hashing, we achieve a final random bit rate of 114 bits/s, with a failure probability less than 10-5.

A fresh look at the way secure communications is currently being done has been undertaken as a consequence of the large hacking's that have taken place recently. A plausible option maybe a return to the future via Morse code using how a quantum bit (Qubit) reacts when entangled to suggest a cypher. This quantum cyphers uses multiple properties of unique entities that have many random radicals which makes hacking more difficult that traditional 'Rivest-Shamir-Adleman' (RSA), 'Digital Signature Algorithm' (DSA) or 'Elliptic Curve Digital Signature Algorithm' (ECDSA). Additional security is likely by Backchannelling (slipstreaming) Quantum Morse code (Q-Morse) keys composed of living and non-living entities. This means Blockchain ledger history (forwards-backwards) is audited during an active session. Verification keys are Backchannelling (slipstreaming) during the session (e.g. train driver must incrementally activate a switch otherwise the train stops) using predicted-expected sender-receiver properties as well as their past history of disconformities to random radicals encountered. In summary, Quantum Morse code (Q-Morse) plausibly is the enabler to additional security by Backchannelling (slipstreaming) during a communications session.

In any security system, there are many security issues that are related to either the sender or the receiver of the message. Quantum computing has proven to be a plausible approach to solving many security issues such as eavesdropping, replay attack and man-in-the-middle attack. In the e-voting system, one of these issues has been solved, namely, the integrity of the data (ballot). In this paper, we propose a scheme that solves the problem of repudiation that could occur when the voter denies the value of the ballot either for cheating purposes or for a real change in the value by a third party. By using an entanglement concept between two parties randomly, the person who is going to verify the ballots will create the entangled state and keep it in a database to use it in the future for the purpose of the non-repudiation of any of these two voters.