De-excitation spectroscopy of strongly interacting Rydberg gases

We present experimental results on the controlled de-excitation of Rydberg states in a cold gas of Rb atoms. The effect of the van der Waals interactions between the Rydberg atoms is clearly seen in the de-excitation spectrum and dynamics. Our observations are confirmed by numerical simulations. In particular, for off-resonant (facilitated) excitation we find that the de-excitation spectrum reflects the spatial arrangement of the atoms in the quasi one-dimensional geometry of our experiment. We discuss future applications of this technique and implications for detection and controlled dissipation schemes.Comment: 6 pages, 5 figure

Naturally-Degradable Photonic Devices with Transient Function by Heterostructured Waxy-Sublimating and Water-Soluble Materials

Combined dry-wet transient materials and devices are introduced, which are based on water-dissolvable dye-doped polymers layered onto non-polar cyclic hydrocarbon sublimating substrates. Light-emitting heterostructures showing amplified spontaneous emission are used as illumination sources for speckle-free, full-field imaging, and transient optical labels are realized that incorporate QR codes with stably encoded information. The transient behavior is also studied at the microscopic scale, highlighting the real time evolution of material domains in the sublimating compound. Finally, the exhausted components are fully soluble in water thus being naturally degradable.Comment: 30 pages, 15 figure

Van der Waals explosion of cold Rydberg clusters

We report on the direct measurement in real space of the effect of the van der Waals forces between individual Rydberg atoms on their external degrees of freedom. Clusters of Rydberg atoms with interparticle distances of around 5μm are created by first generating a small number of seed excitations in a magneto-optical trap, followed by off-resonant excitation that leads to a chain of facilitated excitation events. After a variable expansion time the Rydberg atoms are field ionized, and from the arrival time distributions the size of the Rydberg cluster after expansion is calculated. Our experimental results agree well with a numerical simulation of the van der Waals explosion

Naturally Degradable Photonic Devices with Transient Function by Heterostructured Waxy-Sublimating and Water-Soluble Materials

Combined dry–wet transient materials and devices are introduced, which are based on water-dissolvable dye-doped polymers layered onto nonpolar cyclic hydrocarbon sublimating substrates. Light-emitting heterostructures showing amplified spontaneous emission are obtained on transient elements and used as illumination sources for speckle-free, full-field imaging, and transient optical labels are realized that incorporate QR-codes with stably encoded information. The transient behavior is also studied at the microscopic scale, highlighting the real-time evolution of material domains in the sublimating compound. Finally, the exhausted components are fully soluble in water thus being naturally degradable. This technology opens new and versatile routes for environmental sensing, storage conditions monitoring, and organic photonics

La inteligencia situacional en la formación de adultos : analizando situaciones de aprendizaje para formadores en ciencias sociales

Este libro se dirige a los profesores de ciencias sociales que ejercen la docencia en instituciones de enseñanza superior –administración de empresas, economía, derecho, sociología, psicología, filosofía, teología, etc.– y en diferentes programas –licenciatura, másteres, especializaciones, MBA, EMBA, doctorado, formación continua–. Por lo tanto, se trata de la pedagogía de adultos en situaciones de formación de estudiantes o de desarrollo de directivos. En las disciplinas de ciencias sociales, donde los fundamentos del conocimiento son evolutivos y contingentes, el proceso de aprendizaje-enseñanza es siempre muy complejo, entrando en juego varios enfoques..

Experimental signatures of an absorbing-state phase transition in an open driven many-body quantum system

Understanding and probing phase transitions in non-equilibrium systems is an ongoing challenge in physics. A particular instance are phase transitions that occur between a non-fluctuating absorbing phase, e.g., an extinct population, and one in which the relevant order parameter, such as the population density, assumes a finite value. Here we report the observation of signatures of such a non-equilibrium phase transition in an open driven quantum system. In our experiment rubidium atoms in a quasi one-dimensional cold disordered gas are laser-excited to Rydberg states under so-called facilitation conditions. This conditional excitation process competes with spontaneous decay and leads to a crossover between a stationary state with no excitations and one with a finite number of excitations. We relate the underlying physics to that of an absorbing state phase transition in the presence of a field (i.e. off-resonant excitation processes) which slightly offsets the system from criticality. We observe a characteristic power-law scaling of the Rydberg excitation density as well as increased fluctuations close to the transition point. Furthermore, we argue that the observed transition relies on the presence of atomic motion which introduces annealed disorder into the system and enables the formation of long-ranged correlations. Our study paves the road for future investigations into the largely unexplored physics of non-equilibrium phase transitions in open many-body quantum systems

Real-space measurement of the mechanical effect of the van der Waals-force on Rydberg atoms.

The van der Waals force is the sum of all attractive or repulsive forces between atoms or molecules due to the interactions between permanent or induced dipole moments; it is a topic of widespread interest in many fields of science, such as atomic and condensed matter. physics, chemistry and biology as it is at the basis of very different phenomena, from the complex nature of interatomic and intermolecular interactions, to the characteristic three-dimensional shape of biological macromolecules, to effects in the macroscopic domain such as the capability of geckos to stick on walls without falling. Even if van der Waals force has been known for over a century, it is only in the last few years that experiments targeted to measure the force between two isolated atoms have been carried out: these experiments focus mainly on measuring the effect of the force on internal degrees of freedom of the system, that is the displacement of atomic energy levels due to the interaction. A more direct approach to studying the effect of van der Waals force is to perform measurements on the external degrees of freedom instead, observing the spatial dynamics of the atoms involved in the interaction. However, traditional techniques that have been employed in a lot of experiments in atomic physics through the years, as such those based on fluorescence, cannot be applied in this kind of experiment: in fact, we must deal with small atom numbers, distributed within a large volume of around a cubic millimeter, which the above imaging techniques are not able to detect. Our experiment is performed using an ultracold gas of rubidium atoms trapped in a magneto-optical trap, and we observe the van der Waals force between atoms excited to the 70S Rydberg state, for which the interaction is repulsive. We use Rydberg atoms because, thanks to their larger electrical dipole moments with respect to their ground state counterparts, they lead to larger values of the van der Waals interaction coefficient and thus facilitate the observation of the resulting force. In order to measure the effect of the van der Waals force, we excite about ten atoms in the atomic cloud to the Rydberg state and study their expansion over time by field ionizing them at different moments and gathering information about the arrival times of the corresponding ions to the detector. Our detection technique is based on the analysis of the arrival times of the ions, in a similar way to the study of Coulomb explosions; in order to use this tool we need to make a detailed characterization of our detection apparatus and a calibration of the arrival times. Through this technique we can monitor the spatial expansion of the cloud, as each time we ionize the atoms we take a snapshot of the cloud as it is right before ionization. We also compare the results of the expansions with a numerical simulation without using any free parameter, and a good agreement with the experimental data is achieved. Our experiment represents an innovative approach to the measurement of the van der Waals force using real-space measurements of its mechanical effects, that lead to what may be called a "van der Waals explosion"

Electrophysiological Effects of Hypnosis: Topographical and Source Analysis of Hypnotic Paralysis

This study focuses on brain mechanisms underlying hypnosis. More precisely, we tested the electrophysiological effects of a specific hypnotic suggestion on brain activity. Theoretical models suggested that hypnosis induces inhibition of frontal executive functions but this hypothesis has never been tested with a task requiring inhibition. To assess modulations of inhibitory process, we used an inhibitory Go/Nogo task involving a motor preparation phase, execution and inhibition phase during EEG recordings in two different contexts, normal context and left-hand paralysis context. The paralysis was either suggested by hypnosis for a group of subjects (N=12) or feigned for another group of subjects (N=12). We first performed topographical analyses on the three different phases to assess the modulations of the electric field in relation to hypnotic suggestion. Our results showed that preparatory activity remained similar in terms of topographies, irrespective of the conditions, which suggests that motor intention was preserved during hypnosis. On the contrary, our results revealed a selective topographical modulation in the time-range of the inhibitory P3 component during the hypnotic suggestion of paralysis. As changes in topographies are linked with changes in the configuration of the generators of activity in the brain, we applied in a second time a source analysis on hypnotic conditions, which showed a significant activity in the right middle frontal gyrus in the time-range of P3 component. These results suggest that frontal executive functions are active during hypnosis, which infirm the inhibition hypothesis and shows on the contrary that subjects under hypnosis are not inhibited but that high-level functions are involved in the hypnotic phenomena. Before to present the theoretical background about hypnosis, we briefly defined what is inhibition and how this latter is traditionally measured with cerebral investigation techniques. We present then how hypnosis has been linked with inhibitory process and finally present the purpose of our study. The results are divided into three parts, representing the different analyses: the behavioral results, the topographical results and the source localization results

Experimental studies of the blackbody induced population migration in dissipative Rydberg systems

My work concerns the experimental study of many-body physics using ultracold atoms. Cold atoms experiments represent ideal quantum simulators and allow us to study the complete quantum dynamics of a system under investigation, once its Hamiltonian is known. Among the many implementations, Rydberg atoms, i.e., atoms excited to highly excited states, represent a suitable framework for simulating certain types of physics, such as absorbing state phase transitions and other non-equilibrium phenomena. In fact, Rydberg atoms can naturally implement dissipation through two radiative processes, which are the spontaneous decay and the blackbody induced transitions to neighboring Rydberg states, and its characterization is important for simulations. In my thesis I have developed an experimental method for measuring the lifetimes of high-lying Rydberg states, where the application of traditional techniques results impractical. For this purpose, a detailed characterization of the apparatus, of the detection system and of the electric fields acting on the atoms has been necessary. This measurement allows to distinguish between an initially populated Rydberg state, a target state, from all the other states which are populated through blackbody radiation, the support states. The measurement also allows to obtain the lifetime of the total ensemble of Rydberg atoms in the system. Through this measurement, it is possible to characterize the blackbody induced migration between Rydberg states