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Register a new userQKD: a million signal task
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Authors
Valerio Scarani
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I review the ideas and main results in the derivation of security bounds in quantum key distribution for keys of finite length. In particular, all the detailed studies on specific protocols and implementations indicate that no secret key can be extracted if the number of processed signals per run is smaller than 10^5-10^6. I show how these numbers can be recovered from very basic estimates.
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The transmission and reception of polarized quantum-limited signals from space is of capital interest for a variety of fundamental-physics experiments and quantum-communication protocols. Specifically, Quantum Key Distribution (QKD) deals with the problem of distributing unconditionally-secure cryptographic keys between two parties. Enabling this technology from space is a critical step for developing a truly-secure global communication network. The National Institute of Information and Communications Technology (NICT, Japan) performed the first successful measurement on the ground of a quantum-limited signal from a satellite in experiments carried out on early August in 2016. The SOTA (Small Optical TrAnsponder) lasercom terminal onboard the LEO satellite SOCRATES (Space Optical Communications Research Advanced Technology Satellite) was utilized for this purpose. Two non-orthogonally polarized signals in the ~800-nm band and modulated at 10 MHz were transmitted by SOTA and received in the single-photon regime by using a 1-m Cassegrain telescope on a ground station located in an urban area of Tokyo (Japan). In these experiments, after compensating the Doppler effect induced by the fast motion of the satellite, a QKD-enabling QBER (Quantum Bit Error Rate) below 5% was measured with estimated key rates in the order of several Kbit/s, proving the feasibility of quantum communications in a real scenario from space for the first time.
We propose a method for reconfiguring a relay node for polarization encoded quantum key distribution (QKD) networks. The relay can be switched between trusted and untrusted modes to adapt to different network conditions, relay distances, and security requirements. This not only extends the distance over which a QKD network operates but also enables point-to-multipoint (P2MP) network topologies. The proposed architecture centralizes the expensive and delicate single-photon detectors (SPDs) at the relay node with eased maintenance and cooling while simplifying each user node so that it only needs commercially available devices for low-cost qubit preparation.
Quantum key distribution (QKD) is an ingenious technology utilizing quantum information science for provable secure communication. However, owing to the technological limitations and device non-idealities it is important to analyze the system performance critically and carefully define the implementation security. With an acceleration in the commercial adoption of QKD, a simulation toolkit is requisite to evaluate the functional architecture of QKD protocols. We present a simulation framework to model optical and electrical components for implementing a QKD protocol. The present toolkit aims to model and simulate the optical path of the DPS-QKD protocol with its imperfections and eventually characterize the optical path. The detailed device-level modeling and analysis capabilities of the present toolkit based on Simulink and MATLAB have the potential to provide universal toolkit for practical design and implementation of generalized QKD protocols compared to earlier works. We report a novel work on the implementation of a QKD protocol on Simulink and MATLAB platform. Further, the absence of any modeling framework for DPS QKD and its simplistic optical schematic made it an obvious choice for the authors. We are hopeful that this work will pave way for simulating other QKD protocols from the DPR family.
We propose a novel scheme to implement the BB84 quantum key distribution (QKD) protocol in optical fibers based on a quantum frequency-translation (QFT) process. Unlike conventional QKD systems, which rely on photon polarization/phase to encode qubits, our proposal utilizes photons of different frequencies. Qubits are thus expected to reach longer propagation distances due to the photon frequency state being more robust against mechanical and/or thermal fluctuations of the transmitting medium. Finally, we put forth an extension to a security-enhanced four-character-alphabet (qu-quarts) QKD scheme.
The continuous-variable version of quantum key distribution (QKD) offers the advantages (over discrete-variable systems) of higher secret key rates in metropolitan areas as well as the use of standard telecom components that can operate at room temperature. An important step in the real-world adoption of continuous-variable QKD is the deployment of field tests over commercial fibers. Here we report two different field tests of a continuous-variable QKD system through commercial fiber networks in Xian and Guangzhou over distances of 30.02 km (12.48 dB) and 49.85 km (11.62 dB), respectively. We achieve secure key rates two orders-of-magnitude higher than previous field test demonstrations. This is achieved by developing a fully automatic control system to create stable excess noise and by applying a rate-adaptive reconciliation protocol to achieve a high reconciliation efficiency with high success probability. Our results pave the way to achieving continuous-variable QKD in a metropolitan setting.
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