Physical and architectural considerations in quantum repeaters

Razavi, Mohsen; Thompson, Karen; Farmanbar, Hamid; Piani, Marco; Lütkenhaus, Norbert

doi:10.1117/12.811880

Cited by 15 publications

(15 citation statements)

References 31 publications

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“…The latter would further reduce the secret key generation rate. Our result is somehow different from what is reported in [18,30], although one should bear in mind the different set of assumptions and measures used therein.…”

Section: Nesting Levels and Crossover Distancecontrasting

confidence: 99%

“…The success probability for entanglement distribution between the two memories is, however, M times that of Fig. 4(a).One can show that, the generation rate of entangled states per mode is approximately given by ( 2 3 ) n R ent (L) [18,30]. In our forthcoming analysis, we consider only the case of Fig.…”

Section: E Multimode-memory Configurationmentioning

confidence: 97%

“…4(a) along with the cyclic protocol described in [29,30]. In this protocol, in every cycle of duration L 0 /c, where L 0 is the length of the shortest segment in a quantum repeater and c…”

Section: Multiple-memory Configurationmentioning

confidence: 99%

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Long-distance quantum key distribution with imperfect devices

Piparo

Razavi

2013

Phys. Rev. A

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Quantum key distribution over probabilistic quantum repeaters is addressed. We compare, under practical assumptions, two such schemes in terms of their secret key generation rates per quantum memory. The two schemes under investigation are the one proposed by Duan et al. [Nature (London) 414, 413 (2001)]a n dt h a t of Sangouard et al. [ Phys. Rev. A 76, 050301 (2007)]. We consider various sources of imperfection in both protocols, such as nonzero double-photon probabilities at the sources, dark counts in detectors, and inefficiencies in the channel, photodetectors, and memories. We also consider memory decay and dephasing processes in our analysis. For the latter system, we determine the maximum value of the double-photon probability beyond which secret key distillation is not possible. We also find crossover distances for one nesting level to its subsequent one. We finally compare the two protocols in terms of their achievable secret key generation rates at their optimal settings. Our results specify regimes of operation where one system outperforms the other.

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Section: Nesting Levels and Crossover Distancecontrasting

confidence: 99%

Section: E Multimode-memory Configurationmentioning

confidence: 97%

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Long-distance quantum key distribution with imperfect devices

Piparo

Razavi

2013

Phys. Rev. A

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“…This means that the memory time has to be comparable to the total entanglement creation time. (Razavi et al, 2008) have recently studied quantitatively how the performance of quantum repeaters declines if this is not the case. They find, for example, that the repeater rate declines as a power of exp(− L/cτ ), where L is the total distance, c the speed of light and τ the memory time, in the regime where τ L/c.…”

Section: Storage Timementioning

confidence: 99%

Quantum repeaters based on atomic ensembles and linear optics

et al. 2011

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The distribution of quantum states over long distances is limited by photon loss. Straightforward amplification as in classical telecommunications is not an option in quantum communication because of the no-cloning theorem. This problem could be overcome by implementing quantum repeater protocols, which create long-distance entanglement from shorter-distance entanglement via entanglement swapping. Such protocols require the capacity to create entanglement in a heralded fashion, to store it in quantum memories, and to swap it. One attractive general strategy for realizing quantum repeaters is based on the use of atomic ensembles as quantum memories, in combination with linear optical techniques and photon counting to perform all required operations. Here we review the theoretical and experimental status quo of this very active field. We compare the potential of different approaches quantitatively, with a focus on the most immediate goal of outperforming the direct transmission of photons.

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“…This way, similar to quantum repeaters, we achieve a rate-versus-distance improvement as compared to the MDI-QKD schemes proposed in [18,[28][29][30], or other conventional QKD systems that do not use QMs.There is an important distinction between our protocol and a conventional quantum repeater system that relies on single-mode memories. In such a quantum repeater link, which relies on initial entanglement distribution among neighbouring nodes, the repeat period for the protocol is mainly dictated by the transmission delay for the shortest segment of the repeater system [31,32]. In our scheme, however, the repeat period is constrained by the writing time, including the time needed for the herald/verification process, into memories.…”

mentioning

confidence: 99%

Memory-assisted measurement-device-independent quantum key distribution

et al. 2014

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A protocol with the potential of beating the existing distance records for conventional quantum key distribution (QKD) systems is proposed. It borrows ideas from quantum repeaters by using memories in the middle of the link, and that of measurement-device-independent QKD, which only requires optical source equipment at the userʼs end. For certain memories with short access times, our scheme allows a higher repetition rate than that of quantum repeaters with single-mode memories, thereby requiring lower coherence times. By accounting for various sources of nonideality, such as memory decoherence, dark counts, misalignment errors, and background noise, as well as timing issues with memories, we develop a mathematical framework within which we can compare QKD systems with and without memories. In particular, we show that with the state-of-the-art technology for quantum memories, it is potentially possible to devise memory-assisted QKD systems that, at certain distances of practical interest, outperform current QKD implementations.Keywords: quantum key distribution, quantum memory, measurement device independent, quantum repeaters, quantum networks IntroductionDespite all commercial [1] and experimental achievements in quantum key distribution (QKD) [2-10], reaching arbitrarily long distances is still a remote objective. The fundamental solution to this problem, i.e., quantum repeaters, has been known for over a decade. From early proposals by Briegel et al [11] to the latest no-memory versions [12][13][14], quantum repeaters, typically, rely on highly efficient quantum gates comparable to what we may need for future quantum computers. While the progress on that ground may take some time before such systems become functional, another approach based on probabilistic gate operations was proposed by Duan and co-workers [15], which could offer a simpler way of implementing quantum repeaters for moderate distances of up to around 1000 km. The latter systems require quantum memory (QM) modules with high coupling efficiencies to light and with coherence times exceeding the transmission delays, which are yet to be achieved together. In this paper, we propose a protocol that, although is not as scalable as quantum repeaters, for certain classes of memories, relaxes, to some extent, the harsh requirements on memories' coherence times, thereby paving the way for the existing technologies to beat the highest distance records achieved for no-memory QKD links [2]. The idea behind our protocol was presented in [16], and independent work has also been reported in [17]. This work proposes additional practical schemes and rigorously analyses them under realistic conditions. Our protocol relies on concepts from quantum repeaters, on the one hand, and the recently proposed measurement-device-independent QKD (MDI-QKD), on the other. The original MDI-QKD [18] relies on sending encoded photons by the users to a middle site at which a Bell-state measurement (BSM) is performed. One major practical advantage of MDI-QKD is that this BSM can be...

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Physical and architectural considerations in quantum repeaters

Cited by 15 publications

References 31 publications

Long-distance quantum key distribution with imperfect devices

Long-distance quantum key distribution with imperfect devices

Quantum repeaters based on atomic ensembles and linear optics

Memory-assisted measurement-device-independent quantum key distribution

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