1,264 research outputs found
Sub-Doppler laser cooling of potassium atoms
We investigate sub-Doppler laser cooling of bosonic potassium isotopes, whose
small hyperfine splitting has so far prevented cooling below the Doppler
temperature. We find instead that the combination of a dark optical molasses
scheme that naturally arises in this kind of systems and an adiabatic ramping
of the laser parameters allows to reach sub-Doppler temperatures for small
laser detunings. We demonstrate temperatures as low as 25(3)microK and
47(5)microK in high-density samples of the two isotopes 39K and 41K,
respectively. Our findings will find application to other atomic systems.Comment: 7 pages, 9 figure
Expansion dynamics of a dipolar Bose-Einstein condensate
Our recent measurements on the expansion of a chromium dipolar condensate
after release from an optical trapping potential are in good agreement with an
exact solution of the hydrodynamic equations for dipolar Bose gases. We report
here the theoretical method used to interpret the measurement data as well as
more details of the experiment and its analysis. The theory reported here is a
tool for the investigation of different dynamical situations in time-dependent
harmonic traps.Comment: 12 pages. Submitted to PR
Atom interferometry gravity-gradiometer for the determination of the Newtonian gravitational constant G
We developed a gravity-gradiometer based on atom interferometry for the
determination of the Newtonian gravitational constant \textit{G}. The
apparatus, combining a Rb fountain, Raman interferometry and a juggling scheme
for fast launch of two atomic clouds, was specifically designed to reduce
possible systematic effects. We present instrument performances and show that
the sensor is able to detect the gravitational field induced by source masses.
A discussion of projected accuracy for \textit{G} measurement using this new
scheme shows that the results of the experiment will be significant to
discriminate between previous inconsistent values.Comment: 9 pages,9 figures, Submitte
Crossing Over from Attractive to Repulsive Interactions in a Tunneling Bosonic Josephson Junction
We explore the interplay between tunneling and interatomic interactions in
the dynamics of a bosonic Josephson junction. We tune the scattering length of
an atomic K Bose-Einstein condensate confined in a double-well trap to
investigate regimes inaccessible to other superconducting or superfluid
systems. In the limit of small-amplitude oscillations, we study the transition
from Rabi to plasma oscillations by crossing over from attractive to repulsive
interatomic interactions. We observe a critical slowing down in the oscillation
frequency by increasing the strength of an attractive interaction up to the
point of a quantum phase transition. With sufficiently large initial
oscillation amplitude and repulsive interactions the system enters the
macroscopic quantum self-trapping regime, where we observe coherent undamped
oscillations with a self-sustained average imbalance of the relative well
population. The exquisite agreement between theory and experiments enables the
observation of a broad range of many body coherent dynamical regimes driven by
tunable tunneling energy, interactions and external forces, with applications
spanning from atomtronics to quantum metrology.Comment: 10 pages, 8 figures, supplemental materials are include
Structural connectivity and functional properties of the macaque superior parietal lobule
Despite the consolidated belief that the macaque superior parietal lobule (SPL) is entirely occupied by Brodmann’s area 5, recent data show that macaque SPL also hosts a large cortical region with structural and functional features similar to that of Brodmann’s area 7. According to these data, the anterior part of SPL is occupied by a somatosensory-dominated cortical region that hosts three architectural and functional distinct regions (PE, PEci, PEip) and the caudal half of SPL by a bimodal somato-visual region that hosts four areas: PEc, MIP, PGm, V6A. To date, the most studied areas of SPL are PE, PEc, and V6A. PE is essentially a high-order somatomotor area, while PEc and V6A are bimodal somatomotor–visuomotor areas, the former with predominant somatosensory input and the latter with predominant visual input. The functional properties of these areas and their anatomical connectivity strongly suggest their involvement in the control of limb movements. PE is suggested to be involved in the preparation/execution of limb movements, in particular, the movements of the upper limb; PEc in the control of movements of both upper and lower limbs, as well as in their interaction with the visual environment; V6A in the control of reach-to-grasp movements performed with the upper limb. In humans, SPL is traditionally considered to have a different organization with respect to macaques. Here, we review several lines of evidence suggesting that this is not the case, showing a similar structure for human and non-human primate SPLs
Decoding information for grasping from the macaque dorsomedial visual stream
Neurodecoders have been developed by researchers mostly to control neuroprosthetic devices, but also to shed new light on neural functions. In this study, we show that signals representing grip configurations can be reliably decoded from neural data acquired from area V6A of the monkey medial posterior parietal cortex. Two Macaca fascicularis monkeys were trained to perform an instructed-delay reach-to-grasp task in the dark and in the light toward objects of different shapes. Population neural activity was extracted at various time intervals on vision of the objects, the delay before movement, and grasp execution. This activity was used to train and validate a Bayes classifier used for decoding objects and grip types. Recognition rates were well over chance level for all the epochs analyzed in this study. Furthermore, we detected slightly different decoding accuracies, depending on the task's visual condition. Generalization analysis was performed by training and testing the system during different time intervals. This analysis demonstrated that a change of code occurred during the course of the task. Our classifier was able to discriminate grasp types fairly well in advance with respect to grasping onset. This feature might be important when the timing is critical to send signals to external devices before the movement start. Our results suggest that the neural signals from the dorsomedial visual pathway can be a good substrate to feed neural prostheses for prehensile actions
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