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We review the current status of security proofs for practical decoy-state Quantum Key Distribution using the BB84 protocol, focusing on optical implementations with weak coherent pulses and threshold photodetectors. The primary aim of this…

Quantum Physics · Physics 2025-05-19 Devashish Tupkary , Ernest Y. -Z. Tan , Shlok Nahar , Lars Kamin , Norbert Lütkenhaus

Quantum key distribution (QKD) promises information-theoretic security based on quantum mechanics, but practical implementations face security vulnerabilities due to device imperfections. Recent advances have separately addressed source and…

Quantum Physics · Physics 2025-07-08 Guillermo Currás-Lorenzo , Margarida Pereira , Shlok Nahar , Devashish Tupkary

We develop an improvement to the weak laser pulse BB84 scheme for quantum key distribution, which utilizes entanglement to improve the security of the scheme and enhance its resilience to the photon-number-splitting attack. This protocol…

Measurement-device-independent quantum key distribution (MDIQKD) is a revolutionary protocol since it is physically immune to all attacks on the detection side. However, the protocol still keeps the strict assumptions on the source side…

Phase measurement using a lossless Mach-Zehnder interferometer with certain entangled $N$-photon states can lead to a phase sensitivity of the order of 1/N, the Heisenberg limit. However, previously considered output measurement schemes are…

Quantum Physics · Physics 2009-11-13 Yang Gao , Hwang Lee

In this article we deal with the security of the BB84 quantum cryptography protocol over noisy channels using generalized privacy amplification. For this we estimate the fraction of bits needed to be discarded during the privacy…

Quantum Physics · Physics 2007-05-23 N. Lütkenhaus , Stephen M. Barnett

Unconditional security proofs of the Bennett-Brassard protocol of quantum key distribution have been obtained recently. These proofs cover also practical implementations that utilize weak coherent pulses in the four signal polarizations.…

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

We present a complete protocol for BB84 quantum key distribution for a realistic setting (noise, loss, multi-photon signals of the source) that covers many of todays experimental implementations. The security of this protocol is shown…

Quantum Physics · Physics 2007-07-10 Hitoshi Inamori , Norbert Lütkenhaus , Dominic Mayers

A design is given for an optimized entangling probe attacking the BB84 (Bennett-Brassard 1984) protocol of quantum key distribution and yielding maximum information to the probe for a full range of induced error rates. Probe photon…

Quantum Physics · Physics 2007-05-23 Howard E. Brandt

Imperfect bit-and-basis encoders compromise the security of quantum key distribution (QKD) systems via modulation flaws, side channels and inter-pulse correlations, which invalidate standard security proofs. Existing results addressing such…

Quantum Physics · Physics 2026-02-02 Guillermo Currás-Lorenzo , Margarida Pereira , Go Kato , Marcos Curty , Kiyoshi Tamaki

We consider the mismatched measurements in the BB84 quantum key distribution protocol, in which measuring bases are different from transmitting bases. We give a lower bound on the amount of a secret key that can be extracted from the…

Quantum Physics · Physics 2008-10-17 Ryutaroh Matsumoto , Shun Watanabe

We present a QKD system with fainted pulses using self-homodyne coherent detection in optical fibers at 1543nm. BB84 protocol key is encoded in the optical phase using a twoelectrode Mach-Zehnder modulator, producing a QPSK modulation.

Quantum Physics · Physics 2007-05-23 M. B. Costa e Silva , Q. Xu , S. Agnolini , P. Gallion , F. J. Mendieta

In this paper, we study the unconditional security of the so-called measurement device independent quantum key distribution (MDIQKD) with the basis-dependent flaw in the context of phase encoding schemes. We propose two schemes for the…

Quantum Physics · Physics 2015-06-03 Kiyoshi Tamaki , Hoi-Kwong Lo , Chi-Hang Fred Fung , Bing Qi

In this paper we address the problem of optimizing an unbalanced Mach-Zehnder interferometer, for a given pure input state and considering a specific detection scheme. While the optimum transmission coefficient of the first beam splitter…

Quantum Physics · Physics 2022-08-31 Karunesh K. Mishra , Stefan Ataman

The ideal Bennett-Brassard 1984 (BB84) quantum key distribution protocol is based on the preparation and measurement of qubits in two alternative bases differing by an angle of pi/2. Any real implementation of the protocol, though, will…

Quantum Physics · Physics 2013-03-21 Erik Woodhead , Stefano Pironio

The decoy-state Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol is widely regarded as the de facto standard for practical implementations. On the receiver side, passive basis choice is attractive because it…

Quantum Physics · Physics 2025-11-27 Akihiro Mizutani , Shun Kawakami , Go Kato

The phase uncertainty of an unseeded nonlinear interferometer, where the output of one nonlinear crystal is transmitted to the input of a second crystal that analyzes it, is commonly said to be below the shot-noise level but highly…

Quantum Physics · Physics 2017-12-01 E. Giese , S. Lemieux , M. Manceau , R. Fickler , R. W. Boyd

We prove the unconditional security of a quantum key distribution protocol in which bit values are encoded in the phase of a weak coherent-state pulse relative to a strong reference pulse. In contrast to implementations in which a weak…

Quantum Physics · Physics 2009-11-10 Masato Koashi

We report a single-photon Mach-Zehnder interferometer stabilized to a phase precision of 0.05 degrees over 15 hours. To lock the phase, we employ an auxiliary reference light at a different wavelength than the quantum signal. The developed…

Quantum Physics · Physics 2023-04-12 Vojtěch Švarc , Martina Nováková , Michal Dudka , Miroslav Ježek

The Quantum Key Distribution protocol can encode a single quantum state and implements an information-theoretically secure key distribution protocol in communication. In the actual QKD experimental system, there are usually two encoding…

Quantum Physics · Physics 2020-08-26 Gao Feifei , Li Zhihui , Liu Chengji , Han Duo