arXiv subjects

R. Girard

Publications and source records attributed to R. Girard.

3 recordsLinked to original sources

arXiv2012

A comprehensive design and performance analysis of LEO satellite quantum communication

Optical quantum communication utilizing satellite platforms has the potential to extend the reach of quantum key distribution (QKD) from terrestrial limits of ~200 km to global scales. We have developed a thorough numerical simulation using realistic simulated orbits and incorporating the effects of pointing error, diffraction, atmosphere and telescope design, to obtain estimates of the loss and background noise which a satellite-based system would experience. Combining with quantum optics simulations of sources and detection, we determine the length of secure key for QKD, as well as entanglement visibility and achievable distances for fundamental experiments. We analyze the performance of a low Earth orbit (LEO) satellite for downlink and uplink scenarios of the quantum optical signals. We argue that the advantages of locating the quantum source on the ground justify a greater scientific interest in an uplink as compared to a downlink. An uplink with a ground transmitter of at least 25 cm diameter and a 30 cm receiver telescope on the satellite could be used to successfully perform QKD multiple times per week with either an entangled photon source or with a weak coherent pulse source, as well as perform long-distance Bell tests and quantum teleportation. Our model helps to resolve important design considerations such as operating wavelength, type and specifications of sources and detectors, telescope designs, specific orbits and ground station locations, in view of anticipated overall system performance.

quant-ph↗

arXiv2010

Plugin procedure in segmentation and application to hyperspectral image segmentation

In this article we give our contribution to the problem of segmentation with plug-in procedures. We give general sufficient conditions under which plug in procedure are efficient. We also give an algorithm that satisfy these conditions. We give an application of the used algorithm to hyperspectral images segmentation. Hyperspectral images are images that have both spatial and spectral coherence with thousands of spectral bands on each pixel. In the proposed procedure we combine a reduction dimension technique and a spatial regularisation technique. This regularisation is based on the mixlet modelisation of Kolaczyck and Al.

stat.ML↗

arXiv1997

The role of references in the astronomical discourse

We have counted the number of references in 1179 papers published in Astronomy and Astrophysics over twenty years. The number of references has increased by 60% between 1975 and 1995, reflecting the increase (by the same amount) of the literature which must be cited, and of the number of pages per paper. There are 1.5 times more references in predominantly observational fields than in others. References are used 1.65 times in the text, and there is no trend with time or field. They appear mostly in the introduction (30%) and in the main body of the paper (60%), but papers in predominantly observational fields tend to use less references in the introduction and more in the main body than papers in the other fields. Most references (62%) serve to support a result, and tend to be of theoretical nature. Astronomers are a very conformist bunch, as there are no trends with nationality, and references to conflicting evidence are kept at about 8%. The analysis of a series of papers by de Vaucouleurs on the Hubble constant shows how a controversial subject affects the use of references.

astro-ph↗