Comment on 'Secure Communication using mesoscopic coherent states', Barbosa et al, Phys Rev Lett 90, 227901 (2003)

In a recent letter, Barbosa et al [PRL 90, 227901(2003)] claim that secure communication is possible with bright coherent pulses, by using quantum noise to hide the data from an eavesdropper. We show here that the secrecy in the scheme of Barbosa et al is unrelated to quantum noise, but rather derives from the secret key that sender and receiver share beforehand

Unconditionally secure one-way quantum key distribution using decoy pulses

We report here a complete experimental realization of one-way decoy-pulse quantum key distribution, demonstrating an unconditionally secure key rate of 5.51 kbps for a 25.3 km fibre length. This is two orders of magnitudes higher than the value that can be obtained with a non-decoy system. We introduce also a simple test for detecting the photon number splitting attack and highlight that it is essential for the security of the technique to fully characterize the source and detectors used.Comment: 10 pages, 5 figure

Reply to "Comment on `Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography'"

This is a Reply to the Comment by Lydersen et al. [arXiv: 1106.3756v1]

Quantum key distribution over 122 km of standard telecom fiber

We report the first demonstration of quantum key distribution over a standard telecom fiber exceeding 100 km in length. Through careful optimisation of the interferometer and single photon detector, we achieve a quantum bit error ratio of 8.9% for a 122km link, allowing a secure shared key to be formed after error correction and privacy amplification. Key formation rates of up to 1.9 kbit/sec are achieved depending upon fiber length. We discuss the factors limiting the maximum fiber length in quantum cryptography

Investigation of ship-bank, ship-bottom and ship-ship interactions by using potential flow method

The authors were inspired by the benchmark model test data in MASHCON [1, 2] and carried out some numerical studies on ship-bank, ship-bottom and ship-ship interactions based on potential flow method in the last few years. In the confined waterways, many researchers question the applicability of the classical potential flow method. The main objective of the present paper is to present some validations of the 3D boundary element method (BEM) against the model test data to exam the feasibility of the potential method in predicting the hydrodynamic behaviour of the ships in confined water. The methodology used in the present paper is a 3D boundary element method based on Rankine type Green function. The numerical simulation is based on the in-house developed multi-body hydrodynamic interaction program MHydro. We calculate the wave elevations and forces (or moments) when the ship is manoeuvring in shallow and narrow channel, or when the two ships is travelling side by side or crossing each other. These calculations are compared with the benchmark test data, as well as the published CFD results. Generally, the agreement between the present calculations and model test and CFD results are satisfactory, which indicates that the potential flow method and developed program are still capable to predict the hydrodynamic interaction involved in ship-bank, ship-bottom and ship-ship problem

Avoiding the Detector Blinding Attack on Quantum Cryptography

We show the detector blinding attack by Lydersen et al [1] will be ineffective on most single photon avalanche photodiodes (APDs) and certainly ineffective on any detectors that are operated correctly. The attack is only successful if a redundant resistor is included in series with the APD, or if the detector discrimination levels are set inappropriately