Strong Optomechanical Coupling at Room Temperature by Coherent Scattering

Quantum control of a system requires the manipulation of quantum states faster than any decoherence rate. For mesoscopic systems, this has so far only been reached by few cryogenic systems. An important milestone towards quantum control is the so-called strong coupling regime, which in cavity optomechanics corresponds to an optomechanical coupling strength larger than cavity decay rate and mechanical damping. Here, we demonstrate the strong coupling regime at room temperature between a levitated silica particle and a high finesse optical cavity. Normal mode splitting is achieved by employing coherent scattering, instead of directly driving the cavity. The coupling strength achieved here approaches three times the cavity linewidth, crossing deep into the strong coupling regime. Entering the strong coupling regime is an essential step towards quantum control with mesoscopic objects at room temperature

The Role of Galaxies and Quasars in Reionising the High Redshift Intergalactic Medium

Only one billion years after the Big Bang, the neutral hydrogen in the intergalactic medium had been completely ionised. This last phase transition of the Universe known as the epoch of reionisation is one of the frontiers in astrophysics. Despite our growing knowledge on the timing and topology of cosmic reionisation, the sources responsible for emitting the necessary ionising photons have remained elusive. Specifically, the escape fraction of ionising photons in reionisation-era galaxies and the role of quasars remain open and debated questions. This Thesis aims to answer these questions in order to understand the nature of the sources of reionisation. Firstly, I present the discovery of a luminous galaxy whose double-peak Lyman-α emission profile indicates an escape fraction close to 100%. I show how this galaxy is the first evidence of an object self-ionising its own H II bubble deep into the reionisation era. Secondly, I measure the cross-correlation of z ∼ 5-6 galaxies and metal absorbers with the IGM opacity to Lyman-α probed by high-redshift quasars. I extend the analytical model of the galaxy-IGM cross-correlation to derive average escape fractions for faint galaxies in the reionisation era. Thirdly, I investigate the evolution of quasars with redshift by measuring the relative offsets of broad emission lines in four hundred quasars at 1 < z < 7. I discuss how quasar evolution and selection biases can explain the increased blueshift of the triplyionised carbon (C IV) quasar broad emission line in the first billion years. I then present the first results of a programme to detect missing lensed z ∼ 6 quasars. Finally, this Thesis concludes on the combination of the different results into a coherent picture of the nature of the sources of reionisation and prospects for future instruments and surveys

Image Filtering Using Morphological Amoebas

International audienceThis article presents the use of anisotropic dynamic structuring elements, or amoebas, in order to build content-aware noise reduction filters. The amoeba is the ball defined by a special geodesic distance computed for each pixel, and can be used as a kernel for many kinds of filters and morphological operators. 1. Introduction Noise is possibly the most annoying problem in the field of image processing. There are two ways to work around it: either design particularly robust algorithms that can work in noisy environments, or try to eliminate the noise in a first step while losing as little relevant information as possible and consequently use a normally robust algorithm. There are of course many algorithms that aim at reducing the amount of noise in images. In mathematical morphology filters can be, broadly-speaking, divided into two groups: 1 alternate sequential filters based on morphological openings and clos-ings, that are quite effective but also remove thin elements such as canals or peninsulas. Even worse, they can displace the contours and thus create additional problems in a segmentation application

Covariant Affine Integral Quantization(s)

Covariant affine integral quantization of the half-plane is studied and applied to the motion of a particle on the half-line. We examine the consequences of different quantizer operators built from weight functions on the half-plane. To illustrate the procedure, we examine two particular choices of the weight function, yielding thermal density operators and affine inversion respectively. The former gives rise to a temperature-dependent probability distribution on the half-plane whereas the later yields the usual canonical quantization and a quasi-probability distribution (affine Wigner function) which is real, marginal in both momentum p and position q.Comment: 36 pages, 10 figure