Quantum repeaters and quantum key distribution: The impact of entanglement distillation on the secret key rate

Bratzik, Sylvia; Abruzzo, Silvestre; Kampermann, Hermann; Bruß, Dagmar

doi:10.1103/physreva.87.062335

Cited by 39 publications

(25 citation statements)

References 42 publications

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“…It is hard to make a fair comparison between all these and our scheme, as the required resources in each case are different. Some studies have nevertheless compared different repeater schemes under certain assumptions [64,74]. It is only the future, in the end, that proves which system, and at what price, can be implemented over the course of time.…”

Section: Realistic Examplesmentioning

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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Section: Realistic Examplesmentioning

confidence: 99%

Memory-assisted measurement-device-independent quantum key distribution

et al. 2014

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“…Recently, we investigated the optimal quantum repeater setups with respect to the secret key rate [9,10]. The limiting factor of these quantum repeater schemes, especially regarding the repeater rate, can be the classical communication time to acknowledge the success of entanglement distillation [11].…”

Section: Introductionmentioning

confidence: 99%

“…In this paper we investigate the difference in the secret key rates between the quantum repeater using distillation (generic quantum repeater) and the quantum repeater using quantum error correcting codes (encoded quantum repeater) by employing the analysis developed in [10] for the generic quantum repeater. As a representative for the encoded quantum repeater we choose [11].…”

Section: Introductionmentioning

confidence: 99%

Secret key rates for an encoded quantum repeater

2014

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We investigate secret key rates for the quantum repeater using encoding [L. Jiang et al., Phys. Rev. A 79, 032325 (2009)] and compare them to the standard repeater scheme by Briegel, Dür, Cirac, and Zoller. The former scheme has the advantage of a minimal consumption of classical communication. We analyze the tradeoff in the secret key rate between the communication time and the required resources. For this purpose, we introduce an error model for the repeater using encoding which allows for input Bell states with a fidelity smaller than one, in contrast to the model given in [L. Jiang et al., Phys. Rev. A 79, 032325 (2009)]. We show that one can correct additional errors in the encoded connection procedure of this repeater and develop a suitable decoding algorithm. Furthermore, we derive the rate of producing entangled pairs for the quantum repeater using encoding and give the minimal parameters (gate quality and initial fidelity) for establishing a nonzero secret key. We find that the generic quantum repeater is optimal regarding the secret key rate per memory per second and show that the encoded quantum repeater using the simple three-qubit repetition code can even have an advantage with respect to the resources compared to other recent quantum repeater schemes with encoding.

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“…We therefore conclude that for a realistic repeater implementation over a few hundred kilometers, entanglement purification is unlikely to be beneficial and the best strategy is to focus on high-fidelity implementations without entanglement purification [51,52].…”

Section: Entanglement Purificationmentioning

confidence: 94%

An integrated quantum repeater at telecom wavelength with single atoms in optical fiber cavities

et al. 2016

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Quantum repeaters promise to enable quantum networks over global distances by circumventing the exponential decrease in success probability inherent in direct photon transmission. We propose a realistic, functionally integrated quantum-repeater implementation based on single atoms in optical cavities. Entanglement is directly generated between the single-atom quantum memory and a photon at telecom wavelength. The latter is collected with high efficiency and adjustable temporal and spectral properties into a spatially well-defined cavity mode. It is heralded by a near-infrared photon emitted from a second, orthogonal cavity. Entanglement between two remote quantum memories can be generated via an optical Bell-state measurement, while we propose entanglement swapping based on a highly efficient, cavity-assisted atom-atom gate. Our quantum-repeater scheme eliminates any requirement for wavelength conversion such that only a single system is needed at each node. We investigate a particular implementation with rubidium and realistic parameters for Fabry-Perot cavities based on CO 2 laser-machined optical fibers. We show that the scheme enables the implementation of a rather simple quantum repeater that outperforms direct entanglement generation over large distances and does not require any improvements in technology beyond the state of the art.

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Quantum repeaters and quantum key distribution: The impact of entanglement distillation on the secret key rate

Cited by 39 publications

References 42 publications

Memory-assisted measurement-device-independent quantum key distribution

Memory-assisted measurement-device-independent quantum key distribution

Secret key rates for an encoded quantum repeater

An integrated quantum repeater at telecom wavelength with single atoms in optical fiber cavities

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