Hybrid quantum network design against unauthorized secret-key generation, and its memory cost (original) (raw)
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Information-theoretical security of quantum key distribution (QKD) has been convincingly proven in recent years and remarkable experiments have shown the potential of QKD for real world applications. Due to its unique capability of combining high key rate and security in a realistic finite-size scenario, the efficient version of the BB84 QKD protocol endowed with decoy states has been subject of intensive research. Its recent experimental implementation finally demonstrated a secure key rate beyond 1 Mbps over a 50 km optical fiber. However the achieved rate holds under the restrictive assumption that the eavesdropper performs collective attacks. Here, we review the protocol and generalize its security. We exploit a map by Ahrens to rigorously upper bound the Hypergeometric distribution resulting from a general eavesdropping. Despite the extended applicability of the new protocol, its key rate is only marginally smaller than its predecessor in all cases of practical interest.
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Quantum key distribution (QKD) allows two remote users to establish a secret key in the presence of an eavesdropper. The users share quantum states prepared in two mutually-unbiased bases: one to generate the key while the other monitors the presence of the eavesdropper. Here, we show that a general d-dimension QKD system can be secured by transmitting only a subset of the monitoring states. In particular, we find that there is no loss in the secure key rate when dropping one of the monitoring states. Furthermore, it is possible to use only a single monitoring state if the quantum bit error rates are low enough. We apply our formalism to an experimental d = 4 timephase QKD system, where only one monitoring state is transmitted, and obtain a secret key rate of 17.4 ± 2.8 Mbits/s at a 4 dB channel loss and with a quantum bit error rate of 0.045 ± 0.001 and 0.037 ± 0.001 in time and phase bases, respectively, which is 58.4% of the secret key rate that can be achieved with the full setup. This ratio can be increased, potentially up to 100%, if the error rates in time and phase basis are reduced. Our results demonstrate that it is possible to substantially simplify the design of high-dimensional QKD systems, including those that use the spatial or temporal degrees-of-freedom of the photon, and still outperform qubit-based (d = 2) protocols.
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We investigate how a classical private key can be used by two players, connected by an insecure one-way quantum channel, to perform private communication of quantum information. In particular we show that in order to transmit n qubits privately, 2n bits of shared private key are necessary and sufficient. This result may be viewed as the quantum analogue of the classical one-time pad encryption scheme.
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We develop a model for practical, entanglement-based longdistance quantum key distribution employing entanglement swapping as a key building block. Relying only on existing off-the-shelf technology, we show how to optimize resources so as to maximize secret key distribution rates. The tools comprise lossy transmission links, such as telecom optical fibers or free space, parametric down-conversion sources of entangled photon pairs, and threshold detectors that are inefficient and have dark counts. Our analysis provides the optimal trade-off between detector efficiency and dark counts, which are usually competing, as well as the optimal source brightness that maximizes the secret key rate for specified distances (i.e. loss) between sender and receiver. Practical decoy state for quantum key distribution," Phys. Rev. A 72, 012326 (2005). 21. X.-B. Wang, "Decoy-state protocol for quantum cryptography with four different intensities of coherent light," Phys. Rev. A 72, 012322 (2005). 22. Y. Zhao, B. Qi, X. Ma, H.-K. Lo, and L. Qian, "Experimental Quantum Key Distribution with Decoy States," Phys. Rev. Lett. 96, 070502 (2006). 23. N. Lütkenhaus, "Security against individual attacks for realistic quantum key distribution," Phys. Rev. A 61, 052304 (2000). 24. l.-M. Duan, M. D. Lukin, J. I. Cirac, and P. Zoller, "Long-distance quantum communication with atomic ensembles and linear optics," Nature 414, 413-418, 2001. 25. J. B. Brask and A. S. Sørensen, "Memory imperfections in atomic-ensemble-based quantum repeaters," Phys. Rev. A 78, 012350 (2008). 26. L. Jiang, J. M. Taylor, and M. D. Lukin, "Fast and robust approach to long-distance quantum communication with atomic ensembles," Phys. Rev. A 76, 012301 (2007). -W. Pan, "Robust creation of entanglement between remote memory qubits," Phys. Rev. Lett. 98, 240502 (2007). 28. J. B. Brask, L. Jiang, A. V. Gorshkov, V. Vuletic, A. S. Sørensen, and M. D. Lukin "Fast entanglement distribution with atomic ensembles and fluorescent detection," Phys. Rev. A 81, 020303(R) (2010). 29. J. Amirloo, M. Razavi, and A. H. Majedi, "
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Quantum communications promises reliable transmission of quantum information, efficient distribution of entanglement and generation of completely secure keys. For all these tasks, we need to determine the optimal point-to-point rates that are achievable by two remote parties at the ends of a quantum channel, without restrictions on their local operations and classical communication, which can be unlimited and two-way. These two-way assisted capacities represent the ultimate rates that are reachable without quantum repeaters. Here, by constructing an upper bound based on the relative entropy of entanglement and devising a dimension-independent technique dubbed 'teleportation stretching', we establish these capacities for many fundamental channels, namely bosonic lossy channels, quantum-limited amplifiers, dephasing and erasure channels in arbitrary dimension. In particular, we exactly determine the fundamental rate-loss tradeoff affecting any protocol of quantum key distribut...