SiPM used as fast Photon-Counting Module and for Multiphoton Detection

We demonstrate fast counting and multiphoton detection abilities of a Silicon Photo Multiplier (SiPM). In fast counting mode we are able to detect two consecutive photons separated by only 2.3 ns corresponding to 430 MHz. The counting efficiency for small optical intensities at a wavelength of 532 nm was found to be around 8.3% with a dark count rate of 50 kHz at T=-7 degrees Celsius. Using the SiPM in multiphoton detection mode, we find a good signal discrimination for different numbers of simultaneous detected photons.Comment: 11 pages, 13 figure

Experimental study on Gaussian-modulated coherent states quantum key distribution over standard telecom fiber

In this paper, we present a fully fiber-based one-way Quantum Key Distribution (QKD) system implementing the Gaussian-Modulated Coherent States (GMCS) protocol. The system employs a double Mach-Zehnder Interferometer (MZI) configuration in which the weak quantum signal and the strong Local Oscillator (LO) go through the same fiber between Alice and Bob, and are separated into two paths inside Bob's terminal. To suppress the LO leakage into the signal path, which is an important contribution to the excess noise, we implemented a novel scheme combining polarization and frequency multiplexing, achieving an extinction ratio of 70dB. To further minimize the system excess noise due to phase drift of the double MZI, we propose that, instead of employing phase feedback control, one simply let Alice remap her data by performing a rotation operation. We further present noise analysis both theoretically and experimentally. Our calculation shows that the combined polarization and frequency multiplexing scheme can achieve better stability in practice than the time-multiplexing scheme, because it allows one to use matched fiber lengths for the signal and the LO paths on both sides of the double MZI, greatly reducing the phase instability caused by unmatched fiber lengths. Our experimental noise analysis quantifies the three main contributions to the excess noise, which will be instructive to future studies of the GMCS QKD systems. Finally, we demonstrate, under the "realistic model" in which Eve cannot control the system within Bob's terminal, a secure key rate of 0.3bit/pulse over a 5km fiber link. This key rate is about two orders of magnitude higher than that of a practical BB84 QKD system.Comment: 21 pages, 9 figure

Experimental investigation of a coherent quantum measurement of the degree of polarization of a single mode light beam

A novel method for the direct measurement of the degree of polarization is described. It is one of the first practical implementations of a coherent quantum measurement, the projection on the singlet state. Our first results demonstrate the successful operation of the method. However, due to the nonlinear crystals used presently, its application is limited to spectral widths larger than ~8nm.Comment: 23 pages, 9 figures, submitted to Journal of Modern Optic

Quantum key distribution with "dual detectors"

To improve the performance of a quantum key distribution (QKD) system, high speed, low dark count single photon detectors (or low noise homodyne detectors) are required. However, in practice, a fast detector is usually noisy. Here, we propose a "dual detectors" method to improve the performance of a practical QKD system with realistic detectors: the legitimate receiver randomly uses either a fast (but noisy) detector or a quiet (but slow) detector to measure the incoming quantum signals. The measurement results from the quiet detector can be used to bound eavesdropper's information, while the measurement results from the fast detector are used to generate secure key. We apply this idea to various QKD protocols. Simulation results demonstrate significant improvements in both BB84 protocol with ideal single photon source and Gaussian-modulated coherent states (GMCS) protocol; while for decoy-state BB84 protocol with weak coherent source, the improvement is moderate. We also discuss various practical issues in implementing the "dual detectors" scheme.Comment: 22 pages, 9 figure

Experimental quantum tossing of a single coin

The cryptographic protocol of coin tossing consists of two parties, Alice and Bob, that do not trust each other, but want to generate a random bit. If the parties use a classical communication channel and have unlimited computational resources, one of them can always cheat perfectly. Here we analyze in detail how the performance of a quantum coin tossing experiment should be compared to classical protocols, taking into account the inevitable experimental imperfections. We then report an all-optical fiber experiment in which a single coin is tossed whose randomness is higher than achievable by any classical protocol and present some easily realisable cheating strategies by Alice and Bob.Comment: 13 page

Demonstration of In Silico docking at a large scale on grid infrastructure

présenté par N. Jac

Grid enabled virtual screening against malaria

34 pages, 5 figures, 3 tables, to appear in Journal of Grid Computing - PCSV, à paraître dans Journal of Grid ComputingWISDOM is an international initiative to enable a virtual screening pipeline on a grid infrastructure. Its first attempt was to deploy large scale in silico docking on a public grid infrastructure. Protein-ligand docking is about computing the binding energy of a protein target to a library of potential drugs using a scoring algorithm. Previous deployments were either limited to one cluster, to grids of clusters in the tightly protected environment of a pharmaceutical laboratory or to pervasive grids. The first large scale docking experiment ran on the EGEE grid production service from 11 July 2005 to 19 August 2005 against targets relevant to research on malaria and saw over 41 million compounds docked for the equivalent of 80 years of CPU time. Up to 1,700 computers were simultaneously used in 15 countries around the world. Issues related to the deployment and the monitoring of the in silico docking experiment as well as experience with grid operation and services are reported in the paper. The main problem encountered for such a large scale deployment was the grid infrastructure stability. Although the overall success rate was above 80%, a lot of monitoring and supervision was still required at the application level to resubmit the jobs that failed. But the experiment demonstrated how grid infrastructures have a tremendous capacity to mobilize very large CPU resources for well targeted goals during a significant period of time. This success leads to a second computing challenge targeting Avian Flu neuraminidase N1

HOPE, an open platform for medical data management on the grid

International audienc

Nanoinformatics: developing new computing applications for nanomedicine

Nanoinformatics has recently emerged to address the need of computing applications at the nano level. In this regard, the authors have participated in various initiatives to identify its concepts, foundations and challenges. While nanomaterials open up the possibility for developing new devices in many industrial and scientific areas, they also offer breakthrough perspectives for the prevention, diagnosis and treatment of diseases. In this paper, we analyze the different aspects of nanoinformatics and suggest five research topics to help catalyze new research and development in the area, particularly focused on nanomedicine. We also encompass the use of informatics to further the biological and clinical applications of basic research in nanoscience and nanotechnology, and the related concept of an extended ?nanotype? to coalesce information related to nanoparticles. We suggest how nanoinformatics could accelerate developments in nanomedicine, similarly to what happened with the Human Genome and other -omics projects, on issues like exchanging modeling and simulation methods and tools, linking toxicity information to clinical and personal databases or developing new approaches for scientific ontologies, among many others