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We investigate two-way and one-way single-photon quantum key distribution (QKD) protocols in the presence of loss introduced by the quantum channel. Our analysis is based on a simple precondition for secure QKD in each case. In particular,…

Quantum Physics · Physics 2009-11-13 Marcos Curty , Tobias Moroder

We present an implementation of the time-frequency (TF) quantum key distribution (QKD) protocol realized mainly with standard telecommunication components at 1550 nm. TF-QKD is implemented with modulations in time and frequency, namely…

Quantum Physics · Physics 2021-12-09 Jasper Rödiger , Nicolas Perlot , Oliver Benson , Ronald Freund

Despite its widespread use in fiber optics, encoding quantum information in photonic time-bin states is usually considered impractical for free-space quantum communication as turbulence-induced spatial distortion impedes the analysis of…

Silicon photonics holds the promise of the miniaturization of quantum communication devices. Recently, silicon chip optical transmitters for quantum key distribution (QKD) have been built and demonstrated experimentally. Nonetheless, these…

Quantum Physics · Physics 2018-10-24 Chenyang Li , Marcos Curty , Feihu Xu , Olinka Bedroya , Hoi-Kwong Lo

A prevalent issue in practical applications of quantum key distribution (QKD) is the emergence of correlations among the emitted signals. Although recent works have proved the security of QKD in the presence of this imperfection, they rest…

To prove the security of quantum key distribution (QKD) protocols, several assumptions have to be imposed on users' devices. From an experimental point of view, it is preferable that such theoretical requirements are feasible and the number…

Quantum Physics · Physics 2023-02-07 Akihiro Mizutani

A novel integrated optical source capable of emitting faint pulses with different polarization states and with different intensity levels at 100 MHz has been developed. The source relies on a single laser diode followed by four…

Measurement-device-independent quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on…

Quantum Physics · Physics 2025-12-22 A. P. Pljonkin

Quantum key distribution is unbreakable in theory but may be hacked via imperfections in its hardware implementations. While many imperfections have been mitigated by countermeasures and advanced security proofs, several remain unsolved.…

Quantum Physics · Physics 2026-05-14 Konstantin Zaitsev , Vladimir Bizin , Dmitriy Kuzmin , Vadim Makarov

The decoy-state method is a prominent approach to enhance the performance of quantum key distribution (QKD) systems that operate with weak coherent laser sources. Due to the limited transmissivity of single photons in optical fiber, current…

Quantum Physics · Physics 2026-05-04 Daniil Trefilov , Xoel Sixto , Víctor Zapatero , Anqi Huang , Marcos Curty , Vadim Makarov

There are two main factors limiting the performance of quantum key distribution --- channel transmission loss and noise. Previously, a linear bound was believed to put an upper limit on the rate-transmittance performance. Remarkably, the…

Quantum Physics · Physics 2020-07-01 Pei Zeng , Weijie Wu , Xiongfeng Ma

Quantum key distribution (QKD) has been proved to be information-theoretically secure in theory. Unfortunately, the imperfect devices in practice compromise its security. Thus, to improve the security property of practical QKD systems, a…

Quantum Physics · Physics 2020-10-14 Zhihao Wu , Anqi Huang , Huan Chen , Shi-Hai Sun , Jiangfang Ding , Xiaogang Qiang , Xiang Fu , Ping Xu , Junjie Wu

The problem of security of quantum key protocols is examined. In addition to the distribution of classical keys, the problem of encrypting quantum data and the structure of the operators which perform quantum encryption is studied. It is…

Quantum Physics · Physics 2016-09-08 P. Oscar Boykin

We present an experimental demonstration of a quantum key distribution protocol using coherent polarization states. Post selection is used to ensure a low error rate and security against beam splitting attacks even in the presence of high…

Quantum Physics · Physics 2007-05-23 Stefan Lorenz , Natalia Korolkova , Gerd Leuchs

Quantum key distribution (QKD) can generate secure key bits between remote users with quantum mechanics. However, the gap between the theoretical model and practical realizations gives eavesdroppers opportunities to intercept secret key.…

There has been much interest in quantum key distribution. Experimentally, quantum key distribution over 150 km of commercial Telecom fibers has been successfully performed. The crucial issue in quantum key distribution is its security.…

Quantum Physics · Physics 2009-11-10 Hoi-Kwong Lo , Xiongfeng Ma , Kai Chen

Quantum Key Distribution with the BB84 protocol has been shown to be unconditionally secure even using weak coherent pulses instead of single-photon signals. The distances that can be covered by these methods are limited due to the loss in…

Quantum Physics · Physics 2009-11-10 Marcos Curty , Norbert Lütkenhaus

Entanglement based quantum communication offers an increased level of security in practical secret shared key distribution. One of the fundamental principles enabling this security -- the fact that interfering with one photon will destroy…

Quantum key distribution (QKD) provides information theoretic security based on quantum mechanics, however, its practical deployment is challenged by imperfections of source devices. Among various source loopholes, correlations between…

Quantum key distribution (QKD) with deterministic single photon sources has been demonstrated over intercity fiber and free-space channels. The previous implementations relied mainly on polarization encoding schemes, which are susceptible…