A Quantum Repeater Based on Entanglement Purification and Entanglement Swapping

We discuss a long-distance quantum communication system based on entangled photon pairs, which apply entanglement as its fundamental resource. For distances longer than the coherence length of a counterpart noisy quantum channel, the fidelity of transmission is ordinarily so low that standard purification processes are not applicable. The quantum repeater stretches the length of the entangled photon pairs. And the high fidelity entanglement of photons between sender and receiver is obtained by entanglement purification and entanglement swapping. We compare the nested repeater with the common repeater and show that it outperforms the latter, which is built an EPR pair in less time.

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Teleportation of entanglement over 143 km

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1517007112 ◽

2015 ◽

Vol 112 (46) ◽

pp. 14202-14205 ◽

Cited By ~ 38

Author(s):

Thomas Herbst ◽

Thomas Scheidl ◽

Matthias Fink ◽

Johannes Handsteiner ◽

Bernhard Wittmann ◽

...

Keyword(s):

Direct Consequence ◽

Building Blocks ◽

Entanglement Swapping ◽

Entangled State ◽

Quantum Repeater ◽

Long Distance ◽

Entanglement Purification ◽

Classical Communication ◽

High Loss ◽

La Palma

As a direct consequence of the no-cloning theorem, the deterministic amplification as in classical communication is impossible for unknown quantum states. This calls for more advanced techniques in a future global quantum network, e.g., for cloud quantum computing. A unique solution is the teleportation of an entangled state, i.e., entanglement swapping, representing the central resource to relay entanglement between distant nodes. Together with entanglement purification and a quantum memory it constitutes a so-called quantum repeater. Since the aforementioned building blocks have been individually demonstrated in laboratory setups only, the applicability of the required technology in real-world scenarios remained to be proven. Here we present a free-space entanglement-swapping experiment between the Canary Islands of La Palma and Tenerife, verifying the presence of quantum entanglement between two previously independent photons separated by 143 km. We obtained an expectation value for the entanglement-witness operator, more than 6 SDs beyond the classical limit. By consecutive generation of the two required photon pairs and space-like separation of the relevant measurement events, we also showed the feasibility of the swapping protocol in a long-distance scenario, where the independence of the nodes is highly demanded. Because our results already allow for efficient implementation of entanglement purification, we anticipate our research to lay the ground for a fully fledged quantum repeater over a realistic high-loss and even turbulent quantum channel.

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Entanglement distribution over a 96-km-long submarine optical fiber

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1818752116 ◽

2019 ◽

Vol 116 (14) ◽

pp. 6684-6688 ◽

Cited By ~ 19

Author(s):

Sören Wengerowsky ◽

Siddarth Koduru Joshi ◽

Fabian Steinlechner ◽

Julien R. Zichi ◽

Sergiy M. Dobrovolskiy ◽

...

Keyword(s):

Quantum Physics ◽

Information Science ◽

Global Scale ◽

Great Promise ◽

Quantum Repeater ◽

Long Distance ◽

Optical Telecommunications ◽

Photon Pairs ◽

Telecommunications Network ◽

Entangled Photon Pairs

Quantum entanglement is one of the most extraordinary effects in quantum physics, with many applications in the emerging field of quantum information science. In particular, it provides the foundation for quantum key distribution (QKD), which promises a conceptual leap in information security. Entanglement-based QKD holds great promise for future applications owing to the possibility of device-independent security and the potential of establishing global-scale quantum repeater networks. While other approaches to QKD have already reached the level of maturity required for operation in absence of typical laboratory infrastructure, comparable field demonstrations of entanglement-based QKD have not been performed so far. Here, we report on the successful distribution of polarization-entangled photon pairs between Malta and Sicily over 96 km of submarine optical telecommunications fiber. We observe around 257 photon pairs per second, with a polarization visibility above 90%. Our results show that QKD based on polarization entanglement is now indeed viable in long-distance fiber links. This field demonstration marks the longest-distance distribution of entanglement in a deployed telecommunications network and demonstrates an international submarine quantum communication channel. This opens up myriad possibilities for future experiments and technological applications using existing infrastructure.

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Development of a Quantum Repeater for Long-Distance Quantum Communication Using Photonic Information Storage

10.21236/ada464029 ◽

2007 ◽

Author(s):

Mikhail Lukin

Keyword(s):

Quantum Communication ◽

Information Storage ◽

Quantum Repeater ◽

Long Distance

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A quantum repeater based on decoherence free subspaces

Quantum Information and Computation ◽

10.26421/qic8.5-7 ◽

2008 ◽

Vol 8 (5) ◽

pp. 468-488

Author(s):

U. Dorner ◽

A. Klein ◽

D. Jaksch

Keyword(s):

Quantum Communication ◽

Waiting Times ◽

Entanglement Swapping ◽

Quantum Gates ◽

Quantum Repeater ◽

Decoherence Free Subspace ◽

Decoherence Free Subspaces

We study a quantum repeater which is based on decoherence free quantum gates recently proposed by Klein {\it et al.} [Phys. Rev. A, {\bf 73}, 012332 (2006)]. A number of operations on the decoherence free subspace in this scheme makes use of an ancilla qubit, which undergoes dephasing and thus introduces decoherence to the system. We examine how this decoherence affects entanglement swapping and purification as well as the performance of a quantum repeater. We compare the decoherence free quantum repeater with a quantum repeater based on qubits that are subject to decoherence and show that it outperforms the latter when decoherence due to long waiting times of conventional qubits becomes significant. Thus, a quantum repeater based on decoherence free subspaces is a possibility to greatly improve quantum communication over long or even intercontinental distances.

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Long distance two-party quantum crypto made simple

Quantum Information and Computation ◽

10.26421/qic12.5-6-6 ◽

2012 ◽

Vol 12 (5&6) ◽

pp. 448-460

Author(s):

Iordanis Kerenidis ◽

Stephanie Wehner

Keyword(s):

Quantum Communication ◽

Oblivious Transfer ◽

Difficult Problem ◽

Entanglement Swapping ◽

Quantum States ◽

Large Network ◽

Long Distance ◽

Computational Problem ◽

Cryptographic Primitive

Any two-party cryptographic primitive can be implemented using quantum communication under the assumption that it is difficult to store a large number of quantum states perfectly. However, achieving reliable quantum communication over long distances remains a difficult problem. Here, we consider a large network of nodes with only neighboring quantum links. We exploit properties of this cloud of nodes to enable any two nodes to achieve security even if they are not directly connected. Our results are based on techniques from classical cryptography and do not resort to technologically difficult procedures like entanglement swapping. More precisely, we show that oblivious transfer can be achieved in such a network if and only if there exists a path in the network between the sender and the receiver along which all nodes are honest. Finally, we show that useful notions of security can still be achieved when we relax the assumption of an honest path. For example, we show that we can combine our protocol for oblivious transfer with computational assumptions such that we obtain security if either there exists an honest path, or, as a backup, at least the adversary cannot solve a computational problem.

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Passively stable distribution of polarisation entanglement over 192 km of deployed optical fibre

npj Quantum Information ◽

10.1038/s41534-019-0238-8 ◽

2020 ◽

Vol 6 (1) ◽

Cited By ~ 5

Author(s):

Sören Wengerowsky ◽

Siddarth Koduru Joshi ◽

Fabian Steinlechner ◽

Julien R. Zichi ◽

Bo Liu ◽

...

Keyword(s):

Quantum Key Distribution ◽

Stable Distribution ◽

Dispersion Compensation ◽

Chromatic Dispersion ◽

Bell State ◽

Long Distance ◽

Quantum Networks ◽

Two Photon ◽

Photon Pairs ◽

Entangled Photon Pairs

AbstractQuantum key distribution (QKD) based on entangled photon pairs holds the potential for repeater-based quantum networks connecting clients over long distance. We demonstrate long-distance entanglement distribution by means of polarisation-entangled photon pairs through two successive deployed 96 km-long telecommunications fibres in the same submarine cable. One photon of each pair was detected directly after the source, while the other travelled the fibre cable in both directions for a total distance of 192 km and attenuation of 48 dB. The observed two-photon Bell state exhibited a fidelity 85 ± 2% and was stable over several hours. We employed neither active stabilisation of the quantum state nor chromatic dispersion compensation for the fibre.

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Parameter regimes for surpassing the PLOB bound with error-corrected qudit repeaters

Quantum ◽

10.22331/q-2019-12-16-216 ◽

2019 ◽

Vol 3 ◽

pp. 216 ◽

Cited By ~ 1

Author(s):

Daniel Miller ◽

Timo Holz ◽

Hermann Kampermann ◽

Dagmar Bruß

Keyword(s):

Secure Communication ◽

Quantum Communication ◽

Quantum Repeater ◽

Long Distance ◽

Quantum Networks ◽

Quantum Capacity ◽

Higher Dimensional ◽

Quantum Repeaters ◽

New Applications ◽

Provably Secure

A potential quantum internet would open up the possibility of realizing numerous new applications, including provably secure communication. Since losses of photons limit long-distance, direct quantum communication and wide-spread quantum networks, quantum repeaters are needed. The so-called PLOB-repeaterless bound [Pirandola et al., Nat. Commun. 8, 15043 (2017)] is a fundamental limit on the quantum capacity of direct quantum communication. Here, we analytically derive the quantum-repeater gain for error-corrected, one-way quantum repeaters based on higher-dimensional qudits for two different physical encodings: Fock and multimode qudits. We identify parameter regimes in which such quantum repeaters can surpass the PLOB-repeaterless bound and systematically analyze how typical parameters manifest themselves in the quantum-repeater gain. This benchmarking provides a guideline for the implementation of error-corrected qudit repeaters.

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One-hour coherent optical storage in an atomic frequency comb memory

Nature Communications ◽

10.1038/s41467-021-22706-y ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Yu Ma ◽

You-Zhi Ma ◽

Zong-Quan Zhou ◽

Chuan-Feng Li ◽

Guang-Can Guo

Keyword(s):

Optical Fibers ◽

Large Scale ◽

Quantum Communication ◽

Frequency Comb ◽

Quantum Memory ◽

Spin Coherence ◽

Quantum Repeater ◽

Long Distance ◽

Alternative Solutions ◽

Atomic Frequency

AbstractPhoton loss in optical fibers prevents long-distance distribution of quantum information on the ground. Quantum repeater is proposed to overcome this problem, but the communication distance is still limited so far because of the system complexity of the quantum repeater scheme. Alternative solutions include transportable quantum memory and quantum-memory-equipped satellites, where long-lived optical quantum memories are the key components to realize global quantum communication. However, the longest storage time of the optical memories demonstrated so far is approximately 1 minute. Here, by employing a zero-first-order-Zeeman magnetic field and dynamical decoupling to protect the spin coherence in a solid, we demonstrate coherent storage of light in an atomic frequency comb memory over 1 hour, leading to a promising future for large-scale quantum communication based on long-lived solid-state quantum memories.

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