André Villing

Single Photon Quantum Cryptography

We report the full implementation of a quantum cryptography protocol using a stream of single photon pulses generated by a stable and efficient source operating at room temperature. The single photon pulses are emitted on demand by a single nitrogen-vacancy color center in a diamond nanocrystal. The quantum bit error rate is less that 4.6% and the secure bit rate is 7700 bits/s. The overall performances of our system reaches a domain where single photons have a measurable advantage over an equivalent system based on attenuated light pulses.

Detecting inertial effects with airborne matter-wave interferometry

Inertial sensors relying on atom interferometry offer a breakthrough advance in a variety of applications, such as inertial navigation, gravimetry or ground- and space-based tests of fundamental physics. These instruments require a quiet environment to reach their performance and using them outside the laboratory remains a challenge. Here we report the first operation of an airborne matter-wave accelerometer set up aboard a 0g plane and operating during the standard gravity (1g) and microgravity (0g) phases of the flight. At 1g, the sensor can detect inertial effects more than 300 times weaker than the typical acceleration fluctuations of the aircraft. We describe the improvement of the interferometer sensitivity in 0g, which reaches 2 x 10-4 ms-2 / √Hz with our current setup. We finally discuss the extension of our method to airborne and spaceborne tests of the Universality of free fall with matter waves.

Field test of a continuous-variable quantum key distribution prototype

We have designed and realized a prototype that implements a continuous-variable quantum key distribution (QKD) protocol based on coherent states and reverse reconciliation. The system uses time and polarization multiplexing for optimal transmission and detection of the signal and phase reference, and employs sophisticated error-correction codes for reconciliation. The security of the system is guaranteed against general coherent eavesdropping attacks. The performance of the prototype was tested over preinstalled optical fibres as part of a quantum cryptography network combining different QKD technologies. The stable and automatic operation of the prototype over 57?h yielded an average secret key distribution rate of 8?kbit?s?1 over a 3?dB loss optical fibre, including the key extraction process and all quantum and classical communication. This system is therefore ideal for securing communications in metropolitan size networks with high-speed requirements.

Kinetics of photoinduced gratings by a moving grating technique

Abstract A moving grating technique is used to monitor the kinetics of the amplitudes and phases of the modulations of refractive index and absorption coefficients induced in a photosensitive material by exposure to a system of interference fringes. The analysis is performed here, in the case of thick materials including the slanted geometry, useful for polymeric photorefractive materials. It is illustrated in the case of a photochromic photorefractive crystal. A detailed error analysis is presented for a photochromic DR1 film and a SBN photorefractive crystal.

High-capacity photorefractive neural network implementing a Kohonen topological map

We designed and built a high-capacity neural network based on volume holographic interconnections in a photorefractive crystal. We used this system to implement a Kohonen topological map. We describe and justify our optical setup and present some experimental results of self-organization in the learning database.

Topological map from a photorefractive self-organizing neural network

Abstract We propose and construct an opto-electronic self-organizing neural network able to create a topological map from a learning set of vectors. After the iterative presentation of all vectors, the input of one vector activates a few neurons of the 2D output whose positions indicate the correlation of this vector with the other vectors of the learning set. The system benefits from the specific kinetics of the photorefractive effect to holographically record and update the neural interconnection weights in a photorefractive crystal.

Adaptive photorefractive neurons for self-organizing networks

Abstract Analogies between some learning laws widely used in self-organizing neural networks and the dynamics of hologram creation in photorefractive materials are outlined. Some possible optical implementations of optical neuron units with photorefractive crystals are proposed. These systems present the key characteristics of the adaptive units required for the realization of self-organizing networks. The characteristics, such as feature extraction in a set of images, are experimentally demonstrated.

Photorefractive neural network performing a topological map

In this paper we describe the realization and the operation of a high capacity optoelectronic neural network implementing a classification of vectors through a Kohonen topological map. The setup uses volume holographic interconnects inside a photorefractive crystal to implement the neurons. We show that the system work and is able to classify several tens of vectors.

Automatic classification of images with a photorefractive crystal

We propose a system that takes advantage of volume holographic interconnections and of the particular kinetics of photorefractive crystals. This system is a neural network that implements a Kohonen self-organizing map. It is devoted to the automatic classification of a set of vectors according to their mutual correlations. We present in this paper the problems we encountered while defining and building the experimental setup as well as some solutions we found to improve the system.

Effect Of Compensation On The Amplification Of Photorefractive Two Beam Coupling By Alternating Electric Field

A general expression for the photorefractive gain under step like electric field is derived. It shows the gain dependence on the applied field frequency which is confirmed experimentally. We show how optimum gain enhancement is achieved by adjusting the illumination and the field frequency to the characteristic times of the crystal. Simultaneous contribution of holes and electrons is also considered to explain reduced values of the gain observed in some cases.