210 research outputs found

    A Study of molecular cooling via Sisyphus processes

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    We present a study of Sisyphus cooling of molecules: the scattering of a single-photon remove a substantial amount of the molecular kinetic energy and an optical pumping step allow to repeat the process. A review of the produced cold molecules so far indicates that the method can be implemented for most of them, making it a promising method able to produce a large sample of molecules at sub-mK temperature. Considerations of the required experimental parameters, for instance the laser power and linewidth or the trap anisotropy and dimensionality, are given. Rate equations, as well as scattering and dipolar forces, are solved using Kinetic Monte Carlo methods for several lasers and several levels. For NH molecules, such detailed simulation predicts a 1000-fold temperature reduction and an increase of the phase space density by a factor of 10^7 . Even in the case of molecules with both low Franck-Condon coefficients and a non-closed pumping scheme, 60% of trapped molecules can be cooled from 100 mK to sub-mK temperature in few seconds. Additionally, these methods can be applied to continuously decelerate and cool a molecular bea

    Laser stimulated deexcitation of Rydberg antihydrogen atoms

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    Antihydrogen atoms are routinely formed at CERN in a broad range of Rydberg states. Ground-state anti-atoms, those useful for precision measurements, are eventually produced through spontaneous decay. However given the long lifetime of Rydberg states the number of ground-state antihydrogen atoms usable is small, in particular for experiments relying on the production of a beam of antihydrogen atoms. Therefore, it is of high interest to efficiently stimulate the decay in order to retain a higher fraction of ground-state atoms for measurements. We propose a method that optimally mixes the high angular momentum states with low ones enabling to stimulate, using a broadband frequency laser, the deexcitation toward low-lying states, which then spontaneously decay to ground-state. We evaluated the method in realistic antihydrogen experimental conditions. For instance, starting with an initial distribution of atoms within the n=20‚ąí30n=20-30 manifolds, as formed through charge exchange mechanism, we show that more than 80\% of antihydrogen atoms will be deexcited to the ground-state within 100 ns using a laser producing 2 J at 828 nm.Comment: 10 page

    Phase space density limitation in laser cooling without spontaneous emission

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    We study the possibility to enhance the phase space density of non-interacting particles submitted to a classical laser field without spontaneous emission. We clearly state that, when no spontaneous emission is present, a quantum description of the atomic motion is more reliable than semi-classical description which can lead to large errors especially if no care is taken to smooth structures smaller than the Heisenberg uncertainty principle. Whatever the definition of position - momentum phase space density, its gain is severely bounded especially when started from a thermal sample. More precisely, the maximum phase space density, can only be improved by a factor M for M-level atoms. This bound comes from a transfer between the external and internal degrees of freedom. To circumvent this limit, one can use non-coherent light fields, informational feedback cooling schemes, involve collectives states between fields and atoms, or allow a single spontaneous emission evenComment: 3 figures, 4 page

    Laser Cooling of Molecular Anions

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    We propose a scheme for laser cooling of negatively charged molecules. We briefly summarise the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_2‚ąí\_2^-, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photo-detachment process is present, as well as Doppler laser cooling of trapped C_2‚ąí\_2^-, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources and antimatter physics

    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

    Triplet-singlet conversion by broadband optical pumping

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    We demonstrate the conversion of cold Cs_{2} molecules initially distributed over several vibrational levels of the lowest triplet state a^{3}\Sigma_{u}^{+} into the singlet ground state X^{1}\Sigma_{g}^{+}. This conversion is realized by a broadband laser exciting the molecules to a well-chosen state from which they may decay to the singlet state throug\textcolor{black}{h two sequential single-photon emission steps: Th}e first photon populates levels with mixed triplet-singlet character, making possible a second spontaneous emission down to several vibrational levels of the X^{1}\Sigma_{g}^{+} states. By adding an optical scheme for vibrational cooling, a substantial fraction of molecules are transferred to the ground vibrational level of the singlet state. The efficiency of the conversion process, with and without vibrational cooling, is discussed at the end of the article. The presented conversion is general in scope and could be extended to other molecules.Comment: 5 pages, 4 figure
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