Spectroscopy of atomic rubidium at 500 bar buffer gas pressure: approaching the thermal equilibrium of dressed atom-light states

We have recorded fluorescence spectra of the atomic rubidium D-lines in the presence of several hundreds of bars buffer gas pressure. With additional saturation broadening a spectral linewidth comparable to the thermal energy of the atoms in the heated gas cell is achieved. An intensity-dependent blue asymmetry of the spectra is observed, which becomes increasingly pronounced when extrapolating to infinitely high light intensity. We interpret our results as evidence for the dressed (coupled atom-light) states to approach thermal equilibrium.Comment: 4 page

Resonance beating of light stored using atomic spinor polaritons

We investigate the storage of light in atomic rubidium vapor using a multilevel-tripod scheme. In the system, two collective dark polariton modes exist, forming an effective spinor quasiparticle. Storage of light is performed by dynamically reducing the optical group velocity to zero. After releasing the stored pulse, a beating of the two reaccelerated optical modes is monitored. The observed beating signal oscillates at an atomic transition frequency, opening the way to novel quantum limited measurements of atomic resonance frequencies and quantum switches.Comment: 10 pages, 4 figures; paper title changed, minor corrections implemented

Thermalization of coupled atom-light states in the presence of optical collisions

The interaction of a two-level atomic ensemble with a quantized single mode electromagnetic field in the presence of optical collisions (OC) is investigated both theoretically and experimentally. The main accent is made on achieving thermal equilibrium for coupled atom-light states (in particular dressed states). We propose a model of atomic dressed state thermalization that accounts for the evolution of the pseudo-spin Bloch vector components and characterize the essential role of the spontaneous emission rate in the thermalization process. Our model shows that the time of thermalization of the coupled atom-light states strictly depends on the ratio of the detuning and the resonant Rabi frequency. The predicted time of thermalization is in the nanosecond domain and about ten times shorter than the natural lifetime at full optical power in our experiment. Experimentally we are investigating the interaction of the optical field with rubidium atoms in an ultra-high pressure buffer gas cell under the condition of large atom-field detuning comparable to the thermal energy in frequency units. In particular, an observed detuning dependence of the saturated lineshape is interpreted as evidence for thermal equilibrium of coupled atom-light states. A significant modification of sideband intensity weights is predicted and obtained in this case as well.Comment: 14 pages, 12 figures; the content was edite

{3D} Morphable Face Models -- Past, Present and Future

In this paper, we provide a detailed survey of 3D Morphable Face Models over the 20 years since they were first proposed. The challenges in building and applying these models, namely capture, modeling, image formation, and image analysis, are still active research topics, and we review the state-of-the-art in each of these areas. We also look ahead, identifying unsolved challenges, proposing directions for future research and highlighting the broad range of current and future applications

Elimination, reversal, and directional bias of optical diffraction

We experimentally demonstrate the manipulation of optical diffraction, utilizing the atomic thermal motion in a hot vapor medium of electromagnetically-induced transparency (EIT). By properly tuning the EIT parameters, the refraction induced by the atomic motion may completely counterbalance the paraxial free-space diffraction and by that eliminates the effect of diffraction for arbitrary images. By further manipulation, the diffraction can be doubled, biased asymmetrically to induced deflection, or even reversed. The latter allows an experimental implementation of an analogy to a negative-index lens

A general framework to generate sizing systems from 3D motion data applied to face mask design

For the design of mass-produced wearable objects for a population it is important to find a small number of sizes, called a sizing system, that will fit well on a wide range of individuals in the population. To obtain a sizing system that incorporates the shape of an identity along with its motion, we introduce a general framework to generate a sizing system for dynamic 3D motion data. Based on a registered 3D motion database a sizing system is computed for taskspecific anthropometric measurements and tolerances, specified by designers. We generate the sizing system by transforming the problem into a box stabbing problem, which aims to find the lowest number of points stabbing a set of boxes. We use a standard computational geometry technique to solve this; it recursively computes the stabbing of lower-dimensional boxes. We apply our framework to a database of facial motion data for anthropometric measurements related to the design of face masks. We show the generalization capabilities of this sizing system on unseen data, and compute, for each size, a representative 3D shape that can be used by designers to produce a prototype model

Decoding the Viewpoint and Identity of Faces and Bodies

Our visual system allows us to recognize familiar individuals across different viewpoints, despite large differences in low-level visual information. Previous neuroimaging research has shown that there is a hierarchical organisation across face-responsive brain regions, with lower-level regions representing head viewpoint and higher-level regions representing face identity. In this study, we investigated whether a similar hierarchy is present in body-responsive brain regions, as we also see bodies from many different viewpoints and psychological research has shown we also use information from the body for identification. Furthermore, we investigated whether representations of viewpoint and identity are face and body specific, or generalise to a common representation. We trained participants to recognize three individuals from images of their face and body. We then recorded their brain activity using fMRI while they viewed images of the face and body (shown separately) of the individuals from different viewpoints. Participants responded to the identity or viewpoint, revealing differences in neural representation depending on which feature participants attended to. We found that the occipital face area and extrastriate body area contain representations of face and body viewpoint, and that these viewpoint representations generalize across the face and body (e.g. a classifier trained to distinguish viewpoint of faces could decode viewpoint of bodies). Furthermore, we found that the fusiform body area (FBA) represents body identity in a viewpoint-invariant manner. We decoded face identity in the FBA, and also found a trend in the anterior temporal face area, that has previously been shown to represent face identity. In total, our results show that lower-level face- and body-responsive regions represent viewpoint, and these representations are not driven by low-level visual similarity. We show that the FBA represents body identity, indicating that a similar hierarchy is present for body identity representations in occipitotemporal cortex as has been previously identified for faces

{3D} Morphable Face Models -- Past, Present and Future

International audienceIn this paper, we provide a detailed survey of 3D Morphable Face Models over the 20 years since they were first proposed. The challenges in buildingand applying these models, namely capture, modeling, image formation, and image analysis, are still active research topics, and we review the state-of-the-art in each of these areas. We also look ahead, identifying unsolved challenges, proposing directions for future research and highlighting the broad range of current and future applications