On the efficiency of quantum lithography

Quantum lithography promises, in principle, unlimited feature resolution, independent of wavelength. However, in the literature at least two different theoretical descriptions of quantum lithography exist. They differ in to which extent they predict that the photons retain spatial correlation from generation to the absorption, and while both predict the same feature size, they differ vastly in predicting how efficiently a quantum lithographic pattern can be exposed. Until recently, essentially all experiments reported have been performed in such a way that it is difficult to distinguish between the two theoretical explanations. However, last year an experiment was performed which gives different outcomes for the two theories. We comment on the experiment and show that the model that fits the data unfortunately indicates that the trade-off between resolution and efficiency in quantum lithography is very unfavourable.Comment: 19 pages, extended version including a thorough mathematical derivatio

Decoherence-Free Quantum Information Processing with Four-Photon Entangled States

Decoherence-free states protect quantum information from collective noise, the predominant cause of decoherence in current implementations of quantum communication and computation. Here we demonstrate that spontaneous parametric down-conversion can be used to generate four-photon states which enable the encoding of one qubit in a decoherence-free subspace. The immunity against noise is verified by quantum state tomography of the encoded qubit. We show that particular states of the encoded qubit can be distinguished by local measurements on the four photons only.Comment: 4 pages, 4 eps figures, revtex

Experimental quantum communication complexity

We prove that the fidelity of two exemplary communication complexity protocols, allowing for an N-1 bit communication, can be exponentially improved by N-1 (unentangled) qubit communication. Taking into account, for a fair comparison, all inefficiencies of state-of-the-art set-up, the experimental implementation outperforms the best classical protocol, making it the candidate for multi-party quantum communication applications.Comment: 4 pages, 2 eps figures, RevTEX4; submitted June 23, 200

An improvement of Canny-Deriche filter for ramp edge detection

We present in this paper a generalization of the Canny-Deriche filter for ramp edge detection. The optimisation criteria are those used by Canny (Signal ta noise ratio, Localization and multiple response) . The recursive implementation of the filter gives a stable third order filter and its performances show an increasing of the signal to noise ratio about 20% in the case of blurred and noisy images in comparison with the Deriche filter.Nous présentons dans cet article une généralisation du filtre de Canny-Deriche pour des contours d'images non idéaux. Les critères d'optimisation pour le calcul du filtre sont ceux développés par Cunny (rapport signal sur bruit, localisation et réponse multiple), mais appliqués à un modèle de contour de type exponentiel. Le filtre obtenu est de type récursif d'ordre 3, ss performances illustrent une amélioration de 20% par rapport au filtre de Deriche en ce qui concerne le rapport signal sur bruit d'uns le cas d'images floues et bruitée

Bell's theorem without inequalities and without unspeakable information

A proof of Bell's theorem without inequalities is presented in which distant local setups do not need to be aligned, since the required perfect correlations are achieved for any local rotation of the local setups.Comment: REVTeX4, 4 pages, 1 figure; for Asher Peres' Festschrift, to be published in Found. Phy

Topological Monomodes in non-Hermitian Systems

Topological monomodes have been for long as elusive as magnetic monopoles. The latter was experimentally shown to emerge in effective descriptions of condensed-matter systems, while the experimental exploration of the former has largely been hindered by the complexity of the conceived setups. Here, we present a remarkably simple model and the experimental observation of topological monomodes generated dynamically. By focusing on non-Hermitian one-dimensional (1D) and 2D Su-Schrieffer-Heeger (SSH) models, we theoretically unveil the minimal configuration to realize a topological monomode upon engineering losses and breaking of lattice symmetries. Furthermore, we classify the systems in terms of the (non-Hermitian) symmetries that are present and calculate the corresponding topological invariants. To corroborate the theory, we present experiments in photonic lattices, in which a monomode is observed in the non-Hermitian 1D and 2D SSH models, thus breaking the paradigm that topological corner states should appear in pairs. Our findings might have profound implications for photonics and quantum optics because topological monomodes increase the robustness of corner states by preventing recombination.Comment: 30 (13+17) pages, 17 (4+13) figures, comments are welcom

Practical Decoy State for Quantum Key Distribution

Decoy states have recently been proposed as a useful method for substantially improving the performance of quantum key distribution. Here, we present a general theory of the decoy state protocol based on only two decoy states and one signal state. We perform optimization on the choice of intensities of the two decoy states and the signal state. Our result shows that a decoy state protocol with only two types of decoy states--the vacuum and a weak decoy state--asymptotically approaches the theoretical limit of the most general type of decoy state protocols (with an infinite number of decoy states). We also present a one-decoy-state protocol. Moreover, we provide estimations on the effects of statistical fluctuations and suggest that, even for long distance (larger than 100km) QKD, our two-decoy-state protocol can be implemented with only a few hours of experimental data. In conclusion, decoy state quantum key distribution is highly practical.Comment: 31 pages. 6 figures. Preprint forma

Application de la reconfiguration dynamique des FPGAs : Décodeur arithmétique de JPEG2000

- Cet article a pour sujet l'implantation d'une partie de l'algorithme du standard JPEG2000 (le décodeur arithmétique) dans un FPGA avec l'utilisation de la reconfiguration dynamique. L'implantation sera faite sur l'architecture ARDOISE

Asic implementation of the optimized Canny-Deriche edge detector

We present in this paper the design and the implementation of the optimized Canny-Deriche edge detector. After a brief reminder of the filter's equations, we expose different techniques to speed up the sampling rate of the IIR filter . In particular, to improve throughput rate of the IIR filter, we present a look-ahead with a decomposition technique . This method leads us to design a first chip, which performs over 20 Mhz sampling rate with a silicon area of 60 mm2 . Using a local register retiming method, we have designed a second circuit, which is able to process a pixel in 33 MHz with a silicon area of 30 mm 2 . These two approaches are compared . This work leads us to an ASIC designed in a CMOS 1 p,m technology and succesfully tested .Nous présentons dans cet article l'implantation d'un processeur dédié intégrant le détecteur de contours de Canny-Deriche optimisé. Après un bref rappel des équations du filtre, nous exposons différentes techniques d'accélération des filtres récursifs et notamment une technique d'accélération de calcul par anticipation. Cette méthode nous a amené à la conception d'un premier circuit dont la fréquence de fonctionnement est de l'ordre de 20 Mhz pour une surface de silicium de 60 mm2. En utilisant une méthode de redistribution locale des registres, nous avons réalisé un second circuit, capable de traiter un pixel à une fréquence de 33 MHz pour une surface en silicium inférieure à 30 mm2. Les deux approches sont alors comparées. Cette étude a conduit à la fabrication d'un processeur dédié réalisé en technologie CMOS 1μm, et testé avec succès

Certainty relations between local and nonlocal observables

We demonstrate that for an arbitrary number of identical particles, each defined on a Hilbert-space of arbitrary dimension, there exists a whole ladder of relations of complementarity between local, and every conceivable kind of joint (or nonlocal) measurements. E.g., the more accurate we can know (by a measurement) some joint property of three qubits (projecting the state onto a tripartite entangled state), the less accurate some other property, local to the three qubits, become. We also show that the corresponding complementarity relations are particularly tight for particles defined on prime dimensional Hilbert spaces.Comment: 4 pages, no figure