Long-distance quantum key distribution with imperfect devices

Piparo, Nicolò Lo; Razavi, Mohsen

doi:10.1103/physreva.88.012332

Cited by 18 publications

(27 citation statements)

References 31 publications

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“…In addition to the typical sources of error, such as loss and dark count, the above expressions are functions of misalignment parameters. This misalignment could be a statistical error in the polarization stability of our setup, modelled by e dA and e dB , or an effective misalignment because of memory dephasing [64] and/or background photons. Putting all these effects together, as we have done in appendix D, we obtain Equation (3.8) can also be used in the case of indirectly heralding QMs as explained in appendix D. The main idea is to use the analogy of each leg in figure 1(b) with the original MDI-QKD in figure 1(c).…”

Section: ;mentioning

confidence: 99%

“…We therefore assume that, by driving this memory with short pulses, one can ideally generate the jointly entangled state in equation (2.1) between the memory and a photon [39], where, in this case, | 〉 s H and | 〉 s V are, respectively, the corresponding symmetric collective excited states to horizontal and vertical polarizations [15,37]. By keeping the entangling efficiency low at η = 0.05 ent , here, we try to keep the effect of multiple excitations in such memories low [35,66,64]; further analysis is, however, required to fully account for such effects [45]. We also assume that = T T 2 1 and use the state-of-the-art single-photon detectors with η = 0.93 d at γ = 1 dc count per second and 150 ps of time resolution [67] for all systems.…”

Section: Realistic Examplesmentioning

confidence: 99%

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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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Section: ;mentioning

confidence: 99%

Section: Realistic Examplesmentioning

confidence: 99%

Memory-assisted measurement-device-independent quantum key distribution

et al. 2014

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“…For instance, a click on the non-resolving detector r 0 , and no click on r 1 , can be modeled by the following measurement operator[19] …”

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confidence: 99%

Measurement-Device-Independent Quantum Key Distribution With Ensemble-Based Memories

Piparo

Razavi

Panayi

2015

IEEE J. Select. Topics Quantum Electron.

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Quantum memories are enabling devices for extending the reach of quantum key distribution (QKD) systems. The required specifications for memories are, however, often considered too demanding for available technologies. One can change this mindset by introducing memory-assisted measurement-deviceindependent QKD (MDI-QKD), which imposes less stringent conditions on the memory modules. It has been shown that, in the case of fast single-qubit memories, we can reach rates and distances not attainable by single no-memory QKD links. Single-qubit memories, such as single atoms or ions, have, currently, too slow of an access time to offer an advantage in practice. Here, we relax that assumption, and consider ensemble-based memories, which satisfy the main two requirements of having short access times and large storage-bandwidth products. Our results, however, suggest that the multiple-excitation effects in such memories can be so detrimental that they may wash away the scaling improvement offered by memory-equipped systems. We then propose an alternative setup that can in principle remedy the problem. As a prelude to our main problem, we also obtain secret key generation rates for MDI-QKD systems that rely on imperfect single-photon sources with nonzero probabilities of emitting two photons.Index Terms-Quantum cryptography, measurement-deviceindependent quantum key distribution, quantum memories.

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“…The limitation in going to further distances is dictated by the exponentially-growing loss factor in optical fibers [3]. Probabilistic quantum repeaters offer a solution to extend the communication distance to over thousands of kilometers [4][5][6][7][8][9][10]. However, such quantum repeaters rely on quantum memory modules [11] with characteristics that are hard to achieve with the current technology.…”

Section: Introductionmentioning

confidence: 99%

“…The first of which resembles a noiseless linear amplifier (NLA) [31] and involves an entangling procedure that is based on the method described in [8,32]. Simply, the user's photons are passed through a NLA before storing them into the quantum memories.…”

Section: Introductionmentioning

confidence: 99%

Memory-assisted quantum key distribution resilient against multiple-excitation effects

Piparo

Sinclair

Razavi

2017

Quantum Sci. Technol.

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Memory-assisted measurement-device-independent quantum key distribution (MA-MDI-QKD) has recently been proposed as a technique to improve the rate-versus-distance behavior of QKD systems by using existing, or nearly-achievable, quantum technologies. The promise is that MA-MDI-QKD would require less demanding quantum memories than the ones needed for probabilistic quantum repeaters. Nevertheless, early investigations suggest that, in order to beat the conventional memoryless QKD schemes, the quantum memories used in the MA-MDI-QKD protocols must have high bandwidth-storage products and short interaction times. Among different types of quantum memories, ensemble-based memories offer some of the required specifications, but they typically suffer from multiple excitation effects. To avoid the latter issue, in this paper, we propose two new variants of MA-MDI-QKD both relying on single-photon sources for entangling purposes. One is based on known techniques for entanglement distribution in quantum repeaters. This scheme turns out to offer no advantage even if one uses ideal single-photon sources. By finding the root cause of the problem, we then propose another setup, which can outperform single memory-less setups even if we allow for some imperfections in our single-photon sources. For such a scheme, we compare the key rate for different types of ensemble-based memories and show that certain classes of atomic ensembles can improve the rate-versus-distance behavior.

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Long-distance quantum key distribution with imperfect devices

Cited by 18 publications

References 31 publications

Memory-assisted measurement-device-independent quantum key distribution

Memory-assisted measurement-device-independent quantum key distribution

Measurement-Device-Independent Quantum Key Distribution With Ensemble-Based Memories

Memory-assisted quantum key distribution resilient against multiple-excitation effects

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