1,161 research outputs found
L'homme et l'animal dans le bassin du lac Tchad
Dans le sud du bassin tchadien, la culture du sorgho repiqué - masakwa au Nigeria, muskwari au Nord-Cameroun, berbéré au Tchad - a pris une grande importance dans les systèmes de production et les paysages. L'exemple de trois terroirs montre que son extension s'est accélérée avec l'aggravation des conditions climatiques et l'introduction du coton. La culture de ce sorgho a progressivement sollicité les terres dégagées rapidement par la crue, traditionnellement vouées aux pâturages de saison sèche : la mise en culture de ces terres de décrue paraît une évolution inéluctable. Les éleveurs transhumants sont les grands perdants de cette évolution. Impuissants devant l'augmentation de l'espace cultivé, tant sur les terres exondées que celles inondables, ils semblent contraints de se sédentariser. (Résumé d'auteur
The quantum Rabi model in a superfluid Bose-Einstein condensate
We propose a quantum simulation of the quantum Rabi model in an atomic
quantum dot, which is a single atom in a tight optical trap coupled to the
quasiparticle modes of a superfluid Bose-Einstein condensate. This widely
tunable setup allows to simulate the ultrastrong coupling regime of
light-matter interaction in a system which enjoys an amenable characteristic
timescale, paving the way for an experimental analysis of the transition
between the Jaynes-Cummings and the quantum Rabi dynamics using cold-atom
systems. Our scheme can be naturally extended to simulate multi-qubit quantum
Rabi models. In particular, we discuss the appearance of effective two-qubit
interactions due to phononic exchange, among other features.Comment: Improved version and references adde
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Extracting Semantics of Individual Places from Movement Data by Analyzing Temporal Patterns of Visits
Data reflecting movements of people, such as GPS or GSM tracks, can be a source of information about mobility behaviors and activities of people. Such information is required for various kinds of spatial planning in the public and business sectors. Movement data by themselves are semantically poor. Meaningful information can be derived by means of interactive visual analysis performed by a human expert; however, this is only possible for data about a small number of people. We suggest an approach that allows scaling to large datasets reflecting movements of numerous people. It includes extracting stops, clustering them for identifying personal places of interest (POIs), and creating temporal signatures of the POIs characterizing the temporal distribution of the stops with respect to the daily and weekly time cycles and the time line. The analyst can give meanings to selected POIs based on their temporal signatures (i.e., classify them as home, work, etc.), and then POIs with similar signatures can be classified automatically. We demonstrate the possibilities for interactive visual semantic analysis by example of GSM, GPS, and Twitter data. GPS data allow inferring richer semantic information, but temporal signatures alone may be insufficient for interpreting short stops. Twitter data are similar to GSM data but additionally contain message texts, which can help in place interpretation. We plan to develop an intelligent system that learns how to classify personal places and trips while a human analyst visually analyzes and semantically annotates selected subsets of movement data
Parametric coupling for superconducting qubits
We propose a scheme to couple two superconducting charge or flux qubits
biased at their symmetry points with unequal energy splittings. Modulating the
coupling constant between two qubits at the sum or difference of their two
frequencies allows to bring them into resonance in the rotating frame.
Switching on and off the modulation amounts to switching on and off the
coupling which can be realized at nanosecond speed. We discuss various physical
implementations of this idea, and find that our scheme can lead to rapid
operation of a two-qubit gate.Comment: 6 page
Process tomography of field damping and measurement of Fock state lifetimes by quantum non-demolition photon counting in a cavity
The relaxation of a quantum field stored in a high- superconducting cavity
is monitored by non-resonant Rydberg atoms. The field, subjected to repetitive
quantum non-demolition (QND) photon counting, undergoes jumps between photon
number states. We select ensembles of field realizations evolving from a given
Fock state and reconstruct the subsequent evolution of their photon number
distributions. We realize in this way a tomography of the photon number
relaxation process yielding all the jump rates between Fock states. The damping
rates of the photon states () are found to increase
linearly with . The results are in excellent agreement with theory including
a small thermal contribution
Realization of a superconducting atom chip
We have trapped rubidium atoms in the magnetic field produced by a
superconducting atom chip operated at liquid Helium temperatures. Up to
atoms are held in a Ioffe-Pritchard trap at a distance of 440
m from the chip surface, with a temperature of 40 K. The trap
lifetime reaches 115 s at low atomic densities. These results open the way to
the exploration of atom--surface interactions and coherent atomic transport in
a superconducting environment, whose properties are radically different from
normal metals at room temperature.Comment: Submitted to Phys. Rev. Let
Phase space tweezers for tailoring cavity fields by quantum Zeno dynamics
We discuss an implementation of Quantum Zeno Dynamics in a Cavity Quantum
Electrodynamics experiment. By performing repeated unitary operations on atoms
coupled to the field, we restrict the field evolution in chosen subspaces of
the total Hilbert space. This procedure leads to promising methods for
tailoring non-classical states. We propose to realize `tweezers' picking a
coherent field at a point in phase space and moving it towards an arbitrary
final position without affecting other non-overlapping coherent components.
These effects could be observed with a state-of-the-art apparatus
Microwave probes Dipole Blockade and van der Waals Forces in a Cold Rydberg Gas
We show that microwave spectroscopy of a dense Rydberg gas trapped on a
superconducting atom chip in the dipole blockade regime reveals directly the
dipole-dipole many-body interaction energy spectrum. We use this method to
investigate the expansion of the Rydberg cloud under the effect of repulsive
van der Waals forces and the breakdown of the frozen gas approximation. This
study opens a promising route for quantum simulation of many-body systems and
quantum information transport in chains of strongly interacting Rydberg atoms.Comment: PACS: 03.67.-a, 32.80.Ee, 32.30.-
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