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arXiv:1202.1016 · Physical Review A

Long-distance quantum communication over noisy networks without long-time quantum memory

Paweł Mazurek, Andrzej Grudka, Michał Horodecki, Paweł Horodecki, Justyna Łodyga, Łukasz Pankowski, Anna Przysiężna

Published Dec 4, 2014• 23 citations
arXivHTMLPDF

Abstract

The problem of sharing entanglement over large distances is crucial for implementations of quantum cryptography. A possible scheme for long-distance entanglement sharing and quantum communication exploits networks whose nodes share Einstein-Podolsky-Rosen (EPR) pairs. In Perseguers et al. [Phys. Rev. A 78, 062324 (2008)] the authors put forward an important isomorphism between storing quantum information in a dimension $D$ and transmission of quantum information in a $D+1$-dimensional network. We show that it is possible to obtain long-distance entanglement in a noisy two-dimensional (2D) network, even when taking into account that encoding and decoding of a state is exposed to an error. For 3D networks we propose a simple encoding and decoding scheme based solely on syndrome measurements on 2D Kitaev topological quantum memory. Our procedure constitutes an alternative scheme of state injection that can be used for universal quantum computation on 2D Kitaev code. It is shown that the encoding scheme is equivalent to teleporting the state, from a specific node into a whole two-dimensional network, through some virtual EPR pair existing within the rest of network qubits. We present an analytic lower bound on fidelity of the encoding and decoding procedure, using as our main tool a modified metric on space-time lattice, deviating from a taxicab metric at the first and the last time slices.

DOI
10.1103/physreva.90.062311

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The problem of sharing entanglement over large distances is crucial for implementations of quantum cryptography. A possible scheme for long-distance entanglement sharing and quantum communication exploits networks whose nodes share Einstein-Podolsky-Rosen (EPR) pairs. In Perseguers et al. [Phys. Rev. A 78, 062324 (2008)] the authors put forward an important isomorphism between storing quantum information in a dimension DDD and transmission of quantum information in a D+1D+1D+1-dimensional network. We show that it is possible to obtain long-distance entanglement in a noisy two-dimensional (2D) network, even when taking into account that encoding and decoding of a state is exposed to an error. For 3D networks we propose a simple encoding and decoding scheme based solely on syndrome measurements on 2D Kitaev topological quantum memory. Our procedure constitutes an alternative scheme of state injection that can be used for universal quantum computation on 2D Kitaev code. It is shown that the encoding scheme is equivalent to teleporting the state, from a specific node into a whole two-dimensional network, through some virtual EPR pair existing within the rest of network qubits. We present an analytic lower bound on fidelity of the encoding and decoding procedure, using as our main tool a modified metric on space-time lattice, deviating from a taxicab metric at the first and the last time slices.
The problem of sharing entanglement over large distances is crucial for implementations of quantum cryptography. A possible scheme for long distance entanglement sharing and communication exploits networks, whose nodes share EPR pairs. In [Perseguers et al., Phys. Rev. A 78,062324 (2008)] an important isomorphism between storing quantum information in dimension D and transmission of quantum information in D + 1 network has been put forward. It implies that fault tolerant quantum computing allows in principle for long distance quantum communication. However, in fault-tolerant schemes, one usually considers creating known encoded states. However the process of encoding and decoding is exposed to error. We show that during this stage fidelity drops by a constant factor related to the volume of circuit that replaces a gate, while going to an upper level of concatenation. This shows explicitly, that it is possible to obtain long distance entanglement in 2D network. For 3D networks, much simpler schemes are possible, e.g. due to existence of Kitaev topological quantum memory, shich uses 2D lattice. Again, we consider explicitly the encoding and decoding stages. In [Dennis et al. J. Math. Phys. 43, 4452 (2002)] such scheme was provided in terms of gates. Here we propose a very simple scheme, based solely on syndrome measurements. It is then showed that the scheme is equivalent to teleporting the state to be encoded through some virtual EPR pair existing within the rest of qubits. We then present numerical simulation of performance of such encoding/decoding scheme.
We consider the problem of creating a long-distance entangled state between two stations of a network, where neighboring nodes are connected by noisy quantum channels. We show that any two stations can share an entangled pair if the effective probability for the quantum errors is below a certain threshold, which is achieved by a local encoding of the qubits and a global bit-flip correction. In contrast to the conventional quantum-repeater schemes, we do not need to store the qubits in quantum memory for a long time: our protocol is a one-shot process (i.e., the elementary entangled pairs are used only once) involving one-way classical communication. Furthermore, the overhead of local resources increases only logarithmically with the size of the network, making our proposal favorable to long-distance quantum communication.
In quantum networks, long-distance quantum communication relies on Einstein–Podolsky–Rosen (EPR) pairs. However, EPR pairs undergo decoherence over time, while their on-demand generation incurs latency. Pre-Storing EPR pairs in quantum memories can mitigate this latency, but such memories are costly and scarce resources, making their efficient placement an important design problem. While prior studies have mainly focused on routing or entanglement distribution, the placement of quantum memories under fidelity and purification constraints has received limited attention. In this paper, we propose an optimization framework for quantum memory placement that minimizes the average entanglement generation latency under a limited budget of deployable memories. Simulations across multiple real-world topologies show that our method consistently achieves lower latency than random and centrality-based placements, suggesting its potential to improve the scalability of large-scale quantum communication networks.
Quantum networks (QNs) are expected to play a key role in next-generation networks. A QN is comprised of quantum nodes and links (or bonds) representing entangled qubit pairs (EQPs) shared between two nodes. The probability of establishing a pure maximally entangled pair, known as Einstein-Podolsky-Rosen (EPR) pair, between two neighboring nodes represents the linking probability (or bond occupation probability). If such probability exceeds the so-called percolation threshold, the QN exhibits a percolation phenomenon characterized by the emergence of a giant cluster spanning the entire network. In the presence of such a giant cluster, any two arbitrary nodes in the system are connected by a chain of links with a non-zero probability, thus establishing EPR pairs at remote nodes. This work introduces a procedure for obtaining QNs from initially isolated quantum nodes. In the proposed procedure, two copies of EPR pairs are prepared at a source node and two qubits, one from each pair, are sent to a neighboring node through a noisy quantum channel. Then, a pair of mixed quantum states is established between the source node and the neighboring node. By performing local operations and classical communication, an EPR pair can be established between these two nodes with non-zero probability. Repeating this procedure for every pair of source node and neighboring node, a QN exhibiting a percolation phenomenon can be obtained.
Quantum networks aim to facilitate the fault-tolerant and secure transmission of quantum states across distant devices. The widely adopted quantum teleportation scheme requires multiple rounds of entanglement swapping and purification, leading to significant resource overhead and operational complexity. In this study, we propose a novel fault-tolerant and secure quantum communication scheme based on uncorrectable error injection. Our method exploits a quantum state encoding scheme based on quantum error correction codes, which strategically introduces uncorrectable errors to enhance security. It eliminates the need for entanglement distribution while reducing resource requirements. The injected errors protect against eavesdropping by preventing unauthorized parties from retrieving meaningful information. Security analysis shows that as the data length and encoded message size increase, information leakage becomes negligible relative to the size of the total message. Comparative performance analysis with existing approaches indicates that our method reduces transmission overhead while maintaining comparable fidelity in low-error regimes. These findings suggest that the proposed method offers a scalable and practical alternative for secure long-distance quantum communication, distributed quantum computing, and future quantum internet applications.
Long-range quantum communication and its associated repeater network are a necessity for any future quantum Internet. The performance of such networks is currently limited by the time it takes to establish entangled links between the appropriate parties on the network. Typically this scales as the round trip time for a signal to be transmitted between those parties. We present in this talk the design of a communications network for the direct transfer of quantum information where the rate at which quantum data can be transmitted is not limited by the distance the information needs to be sent but instead by the time to perform efficient local gate operations. Our scheme requires neither the establishment of entanglement between communication nodes nor the use of long-lived quantum memories. Our scheme thus provides a much higher communications rate than in standard teleportation based schemes.