44 research outputs found

    Electric-field induced dipole blockade with Rydberg atoms

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    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

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    Using a non-selective broadband detection scheme we discovered an efficient mechanism of formation of ultracold Cs2_2 molecules in deeply bound levels (v=1‚ąí9v=1-9) of their electronic ground state X1ő£g+^1 \Sigma_g^+. 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 105‚ąí10610^5-10^6 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

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    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

    Non-equilibrium quantum magnetism in a dipolar lattice gas

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    Research on quantum magnetism with ultra-cold gases in optical lattices is expected to open fascinating perspectives for the understanding of fundamental problems in condensed-matter physics. Here we report on the first realization of quantum magnetism using a degenerate dipolar gas in an optical lattice. In contrast to their non-dipolar counterparts, dipolar lattice gases allow for inter-site spin-spin interactions without relying on super-exchange energies, which constitutes a great advantage for the study of spin lattice models. In this paper we show that a chromium gas in a 3D lattice realizes a lattice model resembling the celebrated t-J model, which is characterized by a non-equilibrium spinor dynamics resulting from inter-site Heisenberg-like spin-spin interactions provided by non-local dipole-dipole interactions. Moreover, due to its large spin, chromium lattice gases constitute an excellent environment for the study of quantum magnetism of high-spin systems, as illustrated by the complex spin dynamics observed for doubly-occupied sites.Comment: 10 pages, 5+5 figure

    Observation of collective excitation of two individual atoms in the Rydberg blockade regime

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    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 őľ\mum. 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

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    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

    Dynamique de l'interaction dans un gaz d'atomes de Rydberg froids. Blocage dipolaire, ionisation Penning. Pompage optique et refroidissement de la vibration de molécules

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    The main topic of this thesis deals with electrostatic interactions at very long range between Rydberg atoms. Rydberg atoms provide an extremely large polarizability leading in several configurations to dipole-dipole interactions with range that can reach more than 10 microns. Our high-resolution experiments show an inhibition of excitation when interactions between pairs of Rydberg atoms happen close to a resonance and also using an electric field to control the internal coupling between Rydberg states. These results obtained in a macroscopic ensemble have been transposed to a system of two atoms only (collaboration with Institut d'Optique). We then analyze spatial and temporal dynamics of blockade experiments in presence of an electric field using a kinetic Monte Carlo algorithm and we study the formation of ions and their consequences. Observation of Penning ionization for attractive potentials could lead to the formation of a cold plasma but a similar observation for repulsive potentials between two Rydberg atoms indicates a transfer of population driven by blackbody radiation. A second topic is the study of the formation of cold cesium molecules. Broadband lasers were used to detect these cold molecules and to find new schemes for cooling internal degrees of freedom of the cesium dimer. In the latter case the use of a mode-locked femtosecond laser shaped in intensity and frequency allowed us to populate after a few cycles of absorption-spontaneous emission the vibrational state v = 0 of the electronic ground state of the cesium dimer.Le sujet principal de cette th√®se concerne les interactions √©lectrostatiques √† tr√®s longues port√©s entre atomes de Rydberg. Les atomes de Rydberg offrent une polarisabilit√© extr√™mement importante qui conduit dans plusieurs configurations, √† des interactions de type dip√īle-dip√īle dont la port√©e peut atteindre plus de 10 microns. Nos exp√©riences √† haute r√©solution montrent une inhibition de l'excitation par un contr√īle de l'interaction entre paires d'atomes de Rydberg au voisinage d'une r√©sonance en √©nergie ainsi que par couplage interne entre niveaux de Rydberg lors de l'application d'un champ √©lectrique. Ces r√©sultats obtenus dans un ensemble macroscopique ont √©t√© transpos√©s √† un syst√®me de deux atomes seulement (collaboration avec l'Institut d'Optique). Nous analysons ensuite la dynamique spatiale et temporelle des exp√©riences de blocage dipolaire en champ √©lectrique √† l'aide d'un algorithme Monte Carlo cin√©tique et nous √©tudions la formation d'ions et leurs cons√©quences. L'observation de l'ionisation Penning pour des potentiels attractifs pouvant conduire √† un plasma froid mais aussi pour des potentiels r√©pulsifs entre deux atomes de Rydberg indique un r√īle de transfert du rayonnement thermique. Un deuxi√®me sujet est l'√©tude de la formation de mol√©cules froides de c√©sium. Des lasers √† large bande spectrale ont √©t√© utilis√©s pour la d√©tection de ces mol√©cules froides et dans des sch√©mas de refroidissement des degr√©s de libert√© internes du dim√®re de c√©sium. Dans ce dernier cas l'utilisation d'un laser femtoseconde mode bloqu√© fa√ßonn√© en intensit√© et en fr√©quence nous a permis de peupler apr√®s quelques cycles d'absorption-√©mission spontan√©e l'√©tat vibrationnel v=0 de l'√©tat fondamental du dim√®re de c√©sium

    Dynamique de l'interaction dans un gaz d'atomes de Rydberg froids. Blocage dipolaire, ionisation Penning. Pompage optique et refroidissement de la vibration de molécules

    No full text
    The main topic of this thesis deals with electrostatic interactions at very long range between Rydberg atoms. Rydberg atoms provide an extremely large polarizability leading in several configurations to dipole-dipole interactions with range that can reach more than 10 microns. Our high-resolution experiments show an inhibition of excitation when interactions between pairs of Rydberg atoms happen close to a resonance and also using an electric field to control the internal coupling between Rydberg states. These results obtained in a macroscopic ensemble have been transposed to a system of two atoms only (collaboration with Institut d'Optique). We then analyze spatial and temporal dynamics of blockade experiments in presence of an electric field using a kinetic Monte Carlo algorithm and we study the formation of ions and their consequences. Observation of Penning ionization for attractive potentials could lead to the formation of a cold plasma but a similar observation for repulsive potentials between two Rydberg atoms indicates a transfer of population driven by blackbody radiation. A second topic is the study of the formation of cold cesium molecules. Broadband lasers were used to detect these cold molecules and to find new schemes for cooling internal degrees of freedom of the cesium dimer. In the latter case the use of a mode-locked femtosecond laser shaped in intensity and frequency allowed us to populate after a few cycles of absorption-spontaneous emission the vibrational state v = 0 of the electronic ground state of the cesium dimer.Le sujet principal de cette th√®se concerne les interactions √©lectrostatiques √† tr√®s longues port√©s entre atomes de Rydberg. Les atomes de Rydberg offrent une polarisabilit√© extr√™mement importante qui conduit dans plusieurs configurations, √† des interactions de type dip√īle-dip√īle dont la port√©e peut atteindre plus de 10 microns. Nos exp√©riences √† haute r√©solution montrent une inhibition de l'excitation par un contr√īle de l'interaction entre paires d'atomes de Rydberg au voisinage d'une r√©sonance en √©nergie ainsi que par couplage interne entre niveaux de Rydberg lors de l'application d'un champ √©lectrique. Ces r√©sultats obtenus dans un ensemble macroscopique ont √©t√© transpos√©s √† un syst√®me de deux atomes seulement (collaboration avec l'Institut d'Optique). Nous analysons ensuite la dynamique spatiale et temporelle des exp√©riences de blocage dipolaire en champ √©lectrique √† l'aide d'un algorithme Monte Carlo cin√©tique et nous √©tudions la formation d'ions et leurs cons√©quences. L'observation de l'ionisation Penning pour des potentiels attractifs pouvant conduire √† un plasma froid mais aussi pour des potentiels r√©pulsifs entre deux atomes de Rydberg indique un r√īle de transfert du rayonnement thermique. Un deuxi√®me sujet est l'√©tude de la formation de mol√©cules froides de c√©sium. Des lasers √† large bande spectrale ont √©t√© utilis√©s pour la d√©tection de ces mol√©cules froides et dans des sch√©mas de refroidissement des degr√©s de libert√© internes du dim√®re de c√©sium. Dans ce dernier cas l'utilisation d'un laser femtoseconde mode bloqu√© fa√ßonn√© en intensit√© et en fr√©quence nous a permis de peupler apr√®s quelques cycles d'absorption-√©mission spontan√©e l'√©tat vibrationnel v=0 de l'√©tat fondamental du dim√®re de c√©sium

    Dynamique de l'interaction dans un gaz d'atomes de Rydberg froids

    No full text
    ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
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