43 research outputs found
Electric-field induced dipole blockade with Rydberg atoms
High resolution laser Stark excitation of np (60 < n < 85) Rydberg states of
ultra-cold cesium atoms shows an efficient blockade of the excitation
attributed to long-range dipole-dipole interaction. The dipole blockade effect
is observed as a quenching of the Rydberg excitation depending on the value of
the dipole moment induced by the external electric field. Effects of eventual
ions which could match the dipole blockade effect are discussed in detail but
are ruled out for our experimental conditions. Analytic and Monte-Carlo
simulations of the excitation of an ensemble of interacting Rydberg atoms agree
with the experiments indicates a major role of the nearest neighboring Rydberg
atom.Comment: 4 page
Efficient formation of deeply bound ultracold molecules probed by broadband detection
Using a non-selective broadband detection scheme we discovered an efficient
mechanism of formation of ultracold Cs molecules in deeply bound levels
() of their electronic ground state X. They are formed by
a one-photon photoassociation of ultracold cesium atoms in a manifold of
excited electronic states, followed by a two-step spontaneous emission cascade.
We were able to form about molecules per second in these low
vibrational levels of the ground state. This detection scheme could be
generalized to other molecular species for the systematic investigation of cold
molecule formation mechanisms.Comment: 4 page
Photoionization spectroscopy of excited states of cold cesium dimers
Photoionization spectroscopy of cold cesium dimers obtained by
photoassociation of cold atoms in a magneto-optical trap is reported here. In
particular, we report on the observation and on the spectroscopic analysis of
all the excited states that have actually been used for efficient detection of
cold molecules stabilized in the triplet a^3Sigma_u^+ ground state. They are:
the (1)^3Sigma_g^+ state connected to the 6s+6p asymptote, the (2)^3Sigma_g^+
and (2)^3Pi_g states connected to the 6s+5d asymptote and finally the
(3)^3Sigma_g^+ state connected to the 6s + 7s asymptote. The detection through
these states spans a wide range of laser energies, from 8000 to 16500 cm-1,
obtained with different laser dyes and techniques. Information on the initial
distribution of cold molecules among the different vibrational levels of the
a^3Sigma_u^+ ground state is also provided. This spectroscopic knowledge is
important when conceiving schemes for quantum manipulation, population transfer
and optical detection of cold cesium molecules.Comment: 24 pages, 11 figures. Note: tables are available separately. Accepted
in Molecular Physic
Cooperative excitation and many-body interactions in a cold Rydberg gas
The dipole blockade of Rydberg excitations is a hallmark of the strong
interactions between atoms in these high-lying quantum states. One of the
consequences of the dipole blockade is the suppression of fluctuations in the
counting statistics of Rydberg excitations, of which some evidence has been
found in previous experiments. Here we present experimental results on the
dynamics and the counting statistics of Rydberg excitations of ultra-cold
Rubidium atoms both on and off resonance, which exhibit sub- and
super-Poissonian counting statistics, respectively. We compare our results with
numerical simulations using a novel theoretical model based on Dicke states of
Rydberg atoms including dipole-dipole interactions, finding good agreement
between experiment and theory.Comment: accepted for publication in PRL; 10 pages, 4 figures (including
Supplemental Material
High-fidelity quantum driving
The ability to accurately control a quantum system is a fundamental
requirement in many areas of modern science such as quantum information
processing and the coherent manipulation of molecular systems. It is usually
necessary to realize these quantum manipulations in the shortest possible time
in order to minimize decoherence, and with a large stability against
fluctuations of the control parameters. While optimizing a protocol for speed
leads to a natural lower bound in the form of the quantum speed limit rooted in
the Heisenberg uncertainty principle, stability against parameter variations
typically requires adiabatic following of the system. The ultimate goal in
quantum control is to prepare a desired state with 100% fidelity. Here we
experimentally implement optimal control schemes that achieve nearly perfect
fidelity for a two-level quantum system realized with Bose-Einstein condensates
in optical lattices. By suitably tailoring the time-dependence of the system's
parameters, we transform an initial quantum state into a desired final state
through a short-cut protocol reaching the maximum speed compatible with the
laws of quantum mechanics. In the opposite limit we implement the recently
proposed transitionless superadiabatic protocols, in which the system perfectly
follows the instantaneous adiabatic ground state. We demonstrate that
superadiabatic protocols are extremely robust against parameter variations,
making them useful for practical applications.Comment: 17 pages, 4 figure
Observation of collective excitation of two individual atoms in the Rydberg blockade regime
The dipole blockade between Rydberg atoms has been proposed as a basic tool
in quantum information processing with neutral atoms. Here we demonstrate
experimentally the Rydberg blockade of two individual atoms separated by 4
m. Moreover, we show that, in this regime, the single atom excitation is
enhanced by a collective two-atom behavior associated with the excitation of an
entangled state. This observation is a crucial step towards the deterministic
manipulation of entanglement of two or more atoms using the Rydberg dipole
interaction.Comment: 5 pages, 4 figure
Kinetic Monte Carlo modelling of dipole blockade in Rydberg excitation experiment
We present a method to model the interaction and the dynamics of atoms
excited to Rydberg states. We show a way to solve the optical Bloch equations
for laser excitation of the frozen gas in good agreement with the experiment. A
second method, the Kinetic Monte Carlo method gives an exact solution of rate
equations. Using a simple N-body integrator (Verlet), we are able to describe
dynamical processes in space and time. Unlike more sophisticated methods, the
Kinetic Monte Carlo simulation offers the possibility of numerically following
the evolution of tens of thousands of atoms within a reasonable computation
time. The Kinetic Monte Carlo simulation gives good agreement with
dipole-blockade type of experiment. The role of ions and the individual
particle effects are investigated.Comment: 23 pages. Submitted to New Journal of Physic
Pompage optique et refroidissement laser de la vibration de molecules froides
This Thesis deals with different studies on the formation and detection of cold molecules. Different long range molecular states, for the Cs2 molecule, are studied by photoassociation and ionization spectroscopy. This different studies permit to improve our knowledge of cold atoms photoassociation mechanisms, created molecule in the triplet fundamental state (a 3Σu+).A non-selective detection has been developed to search mechanisms produce molecules in the singlet fundamental state with few vibration energy. With this new detection, a new formation of molecule mechanism has been founded. This one permit to efficiently produce molecule in a level distribution with very few vibration in the fundamental state (X 1Σg+).Using a shaped femtoseconde laser (broadband laser), vibrational cooling of molecules have been demonstrated, allows the formation of cold molecules without vibration. This femtoseconde laser permits to excited several vibrational levels (originally created by photoassociation) and so realise a optical pumping of molecules. The laser is shaped to remove the frequency corresponding to the transition with the level of zero vibration, and accumulate all the molecules in this only one state.This result is also simulated with a simple theoretic model. This simulation permit to extend this idea for the cooling of the rotation of the molecule.A part (summarised) show, with different published articles, the studies about the long range dipole-dipole interactions between Rydberg atoms, and the ionization process in a cold Rydberg gas.Cette thÚse présente différentes études sur la formation et la détection de molécules froides. Différents états moléculaires de grandes élongations, pour la molécule Cs2, sont étudié par spectroscopie de photoassociation et d'ionisation. Ces différentes études ont permis d'affiner notre compréhension des mécanismes de photoassociation d'atomes froids formant des molécules dans l'état fondamental triplet (a 3Σu+).Une détection non sélective a été développée, pour la recherche de mécanismes de formation de molécules froides dans l'état fondamental singulet avec peu de vibration. Avec cette nouvelle détection, un nouveau mécanisme de formation de molécules par photoassociation d'atomes froids de césium a été trouvé. Celui-ci permet de former efficacement des molécules dans une distribution de niveaux avec trÚs peu de vibration dans l'état fondamental (X 1Σg+).En utilisant un laser femtoseconde (large spectralement) façonné, un refroidissement vibrationnel des molécules a été démontré, permettant la formation de molécules froides sans vibrations. Le laser femtoseconde, permet d'exciter les nombreux niveaux vibrationnels, créés par photoassociation, il réalise ainsi un pompage optique des molécules. Le laser est façonné de maniÚre à rendre l'état de vibration zéro, noir pour ce laser, et ainsi accumuler toutes les molécules vers ce seul état. Ce résultat est également simulé par un model théorique simple. Cette simulation permet de généraliser l'idée au refroidissement de la rotation des molécules. Une partie (résumée) présente, en s'appuyant sur les différents articles publiés, les études sur les interactions dipÎle-dipÎle, à grandes portées, entre atomes de Rydberg
Pompage optique et refroidissement laser de la vibration de molécules froides
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