Entanglement purification with noisy apparatus can be used to factor out an eavesdropper

Safeguarding Quantum Key Distribution through Detection Randomization

We propose and experimentally demonstrate a scheme to render the detection apparatus of a Quantum Key Distribution system immune to the main classes of hacking attacks in which the eavesdropper explores the back-door opened by the single-photon detectors. The countermeasure is based on the creation of modes that are not deterministically accessible to the eavesdropper. We experimentally show that the use of beamsplitters and extra single-photon detectors at the receiver station passively creates randomized spatial modes that erase any knowledge the eavesdropper might have gained when using bri…

On the QKD relaying models

We investigate Quantum Key Distribution (QKD) relaying models. Firstly, we propose a novel quasi-trusted QKD relaying model. The quasi-trusted relays are defined as follows: (i) being honest enough to correctly follow a given multi-party finite-time communication protocol; (ii) however, being under the monitoring of eavesdroppers. We develop a simple 3-party quasi-trusted model, called Quantum Quasi-Trusted Bridge (QQTB) model, to show that we could securely extend up to two times the limited range of single-photon based QKD schemes. We also develop the Quantum Quasi-Trusted Relay (QQTR) model…

Security proof of Counterfactual Quantum Cryptography against General Intercept-resend Attacks and Its Vulnerability

Counterfactual quantum cryptography (CQC), recently proposed by Noh, is featured with no transmission of signal particles. This exhibits evident security advantage, such as its immunity to the well known PNS attack. In this paper, the theoretical security of CQC protocol against the general intercept-resend attacks is proved by bounding the information of an eavesdropper Eve more tightly than in Yin's proposal[Phys. Rev. A 82, 042335 (2010)]. It is also showed that practical CQC implementations may be vulnerable when equipped with imperfect apparatuses, by proving that a negative key rate can …

二分界信息存在

Bipartite Bound Information Exists

研究经典密码学中是否存在类似量子束缚纠缠的现象即界信息。通过证明给出两个比特和一个三进制位分布的例子，利用比较窃听者方式的差距。还表明束缚纠缠三量子比特态标准基测量非此例，其纯化态其他测量可产生界信息。

Quantum privacy amplification and the security of quantum cryptography over noisy channels

Existing quantum cryptographic schemes are not, as they stand, operable in the presence of noise on the quantum communication channel. Although they become operable if they are supplemented by classical privacy-amplification techniques, the resulting schemes are difficult to analyse and have not been proved secure. We introduce the concept of quantum privacy amplification and a cryptographic scheme incorporating it which is provably secure over a noisy channel. The scheme uses an `entanglement purification' procedure which, because it requires only a few quantum Controlled-Not and single-qubit…

监控噪声量子动力学中的混合态可学习性转变

Mixed-state learnability transitions in monitored noisy quantum dynamics

研究在噪声监控量子动力学中混合态可学习性转变，发现两种信息论相并通过张量网络高效模拟。

Distillation of secret key and entanglement from quantum states

We study and solve the problem of distilling secret key from quantum states representing correlation between two parties (Alice and Bob) and an eavesdropper (Eve) via one-way public discussion: we prove a coding theorem to achieve the "wire-tapper" bound, the difference of the mutual information Alice-Bob and that of Alice-Eve, for so-called cqq-correlations, via one-way public communication. This result yields information--theoretic formulas for the distillable secret key, giving ``ultimate'' key rate bounds if Eve is assumed to possess a purification of Alice and Bob's joint state. Specialis…

有限窃听条件下实用光纤连续变量量子密钥分发的安全性分析

The Security Analysis of Continuous-Variable Quantum Key Distribution under Limited Eavesdropping with Practical Fiber

本文基于隐形传态集体攻击模型，分析实用光纤损耗对连续变量QKD窃听能力的影响，发现有限纠缠下最优攻击为单站近发射端攻击，实际密钥率可提升20%~40%，且光纤损耗总体上有利于实际系统安全性与性能。