Symmetric and asymmetric quantum channels in quantum communication systems

Decoherence is one of the main obstacles in quantum information processing. In cryptographic scenarios, in particular, decoherence is not only responsible for the loss of the quantum properties but also for information leakage out to a wiretapper. Given that decoherence must be fought in real-world quantum communication systems, we present a scheme, using decoherence-free subspaces and subsystems, to perform secure classical communications through noisy quantum channels. Using quantum information and wiretap theories, we establish a proof of unconditional security of our scheme. We illustrate our proposal with a non-trivial example and discuss some of its impacts on already existing quantum secure message exchange protocols. Furthermore, we present some up-to-date technologies that can be used for practical implementation of the scheme proposed.

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Optimal teleportation via noisy quantum channels without additional qubit resources

npj Quantum Information ◽

10.1038/s41534-021-00426-x ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Dong-Gil Im ◽

Chung-Hyun Lee ◽

Yosep Kim ◽

Hyunchul Nha ◽

M. S. Kim ◽

...

Keyword(s):

Quantum Computing ◽

Quantum Teleportation ◽

Quantum Communication ◽

Quantum Noise ◽

Single Copy ◽

Entangled State ◽

Quantum Network ◽

Quantum Channels ◽

Maximally Entangled State ◽

Near Term

AbstractQuantum teleportation exemplifies how the transmission of quantum information starkly differs from that of classical information and serves as a key protocol for quantum communication and quantum computing. While an ideal teleportation protocol requires noiseless quantum channels to share a pure maximally entangled state, the reality is that shared entanglement is often severely degraded due to various decoherence mechanisms. Although the quantum noise induced by the decoherence is indeed a major obstacle to realizing a near-term quantum network or processor with a limited number of qubits, the methodologies considered thus far to address this issue are resource-intensive. Here, we demonstrate a protocol that allows optimal quantum teleportation via noisy quantum channels without additional qubit resources. By analyzing teleportation in the framework of generalized quantum measurement, we optimize the teleportation protocol for noisy quantum channels. In particular, we experimentally demonstrate that our protocol enables to teleport an unknown qubit even via a single copy of an entangled state under strong decoherence that would otherwise preclude any quantum operation. Our work provides a useful methodology for practically coping with decoherence with a limited number of qubits and paves the way for realizing noisy intermediate-scale quantum computing and quantum communication.

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An approach for security evaluation and certification of a complete quantum communication system

Scientific Reports ◽

10.1038/s41598-021-84139-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Shihan Sajeed ◽

Poompong Chaiwongkhot ◽

Anqi Huang ◽

Hao Qin ◽

Vladimir Egorov ◽

...

Keyword(s):

Communication Systems ◽

Distribution Systems ◽

Quantum Communication ◽

Global Scale ◽

Security Evaluation ◽

Wave System ◽

System Implementation ◽

Optical Part ◽

Quantum Optical ◽

Complete Quantum

AbstractAlthough quantum communication systems are being deployed on a global scale, their realistic security certification is not yet available. Here we present a security evaluation and improvement protocol for complete quantum communication systems. The protocol subdivides a system by defining seven system implementation sub-layers based on a hierarchical order of information flow; then it categorises the known system implementation imperfections by hardness of protection and practical risk. Next, an initial analysis report lists all potential loopholes in its quantum-optical part. It is followed by interactions with the system manufacturer, testing and patching most loopholes, and re-assessing their status. Our protocol has been applied on multiple commercial quantum key distribution systems to improve their security. A detailed description of our methodology is presented with the example of a subcarrier-wave system. Our protocol is a step towards future security evaluation and security certification standards.

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An Intelligent Link Selection Mechanism for Hybrid Classical-Quantum Communication Systems

IEEE Communications Letters ◽

10.1109/lcomm.2021.3129792 ◽

2021 ◽

pp. 1-1

Author(s):

Shantom Kumar Borah ◽

Sainath Bitragunta

Keyword(s):

Communication Systems ◽

Quantum Communication ◽

Selection Mechanism ◽

Classical Quantum

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Synchronization of quantum communication systems based on correlated photons

10.1364/cleo_at.2021.atu1s.3 ◽

2021 ◽

Author(s):

Christopher Spiess ◽

Sebastian Töpfer ◽

Sakshi Sharma ◽

Andrej Krzic ◽

Gregor Sauer ◽

...

Keyword(s):

Communication Systems ◽

Quantum Communication

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Performance characterization of Pauli channels assisted by indefinite causal order and post-measurement

Quantum Information and Computation ◽

10.26421/qic20.15-16-1 ◽

2020 ◽

Vol 20 (15&16) ◽

pp. 1261-1280

Author(s):

Francisco Delgado ◽

Carlos Cardoso-Isidoro

Keyword(s):

Quantum Channel ◽

Communication Channel ◽

Quantum Communication ◽

Quantum Channels ◽

Causal Order ◽

Combined Process ◽

Performance Characterization ◽

Output State ◽

Transmission Of Information

Indefinite causal order has introduced disruptive procedures to improve the fidelity of quantum communication by introducing the superposition of { orders} on a set of quantum channels. It has been applied to several well characterized quantum channels as depolarizing, dephasing and teleportation. This work analyses the behavior of a parametric quantum channel for single qubits expressed in the form of Pauli channels. Combinatorics lets to obtain affordable formulas for the analysis of the output state of the channel when it goes through a certain imperfect quantum communication channel when it is deployed as a redundant application of it under indefinite causal order. In addition, the process exploits post-measurement on the associated control to select certain components of transmission. Then, the fidelity of such outputs is analysed to characterize the generic channel in terms of its parameters. As a result, we get notable enhancement in the transmission of information for well characterized channels due to the combined process: indefinite causal order plus post-measurement.

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Twisted photon entanglement through turbulent air across Vienna

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1517574112 ◽

2015 ◽

Vol 112 (46) ◽

pp. 14197-14201 ◽

Cited By ~ 88

Author(s):

Mario Krenn ◽

Johannes Handsteiner ◽

Matthias Fink ◽

Robert Fickler ◽

Anton Zeilinger

Keyword(s):

Angular Momentum ◽

Quantum Entanglement ◽

Quantum Communication ◽

Entangled States ◽

Phase Front ◽

Quantum Channels ◽

Long Distance ◽

Large Alphabet ◽

Large State Space ◽

Promising Application

Photons with a twisted phase front can carry a discrete, in principle, unbounded amount of orbital angular momentum (OAM). The large state space allows for complex types of entanglement, interesting both for quantum communication and for fundamental tests of quantum theory. However, the distribution of such entangled states over large distances was thought to be infeasible due to influence of atmospheric turbulence, indicating a serious limitation on their usefulness. Here we show that it is possible to distribute quantum entanglement encoded in OAM over a turbulent intracity link of 3 km. We confirm quantum entanglement of the first two higher-order levels (with OAM=± 1ℏ and ± 2ℏ). They correspond to four additional quantum channels orthogonal to all that have been used in long-distance quantum experiments so far. Therefore, a promising application would be quantum communication with a large alphabet. We also demonstrate that our link allows access to up to 11 quantum channels of OAM. The restrictive factors toward higher numbers are technical limitations that can be circumvented with readily available technologies.

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