Rovibrational optical cooling of a molecular beam

Cooling the rotation and the vibration of molecules by broadband light sources was possible for trapped molecular ions or ultracold molecules. Because of a low power spectral density, the cooling timescale has never fell below than a few milliseconds. Here we report on rotational and vibrational cooling of a supersonic beam of barium monofluoride molecules in less than 440 $\mu$s. Vibrational cooling was optimized by enhancing the spectral power density of a semiconductor light source at the underlying molecular transitions allowing us to transfer all the populations of $v''=1-3$ into the vibrational ground state ($v''=0$). Rotational cooling, that requires an efficient vibrational pumping, was then achieved. According to a Boltzmann fit, the rotation temperature was reduced by almost a factor of 10. In this fashion, the population of the lowest rotational levels increased by more than one order of magnitude

Atom-molecule collisions in an optically trapped gas

Cold inelastic collisions between confined cesium (Cs) atoms and Cs$\_2$ molecules are investigated inside a CO$\_2$ laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of $\sim 2.5 \times 10^{-11}$cm$^3$ s$^{-1}$, mainly independent of the molecular ro-vibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime ranges 0,3-1 s, four times smaller than the atomic one, as is also observed in a pure magnetic trap. We give an estimation of the inelastic molecule-molecule collision rate to be $\sim 10^{-11}$ cm$^{3}$ s$^{-1}$

Optimized production of large Bose Einstein Condensates

We suggest different simple schemes to efficiently load and evaporate a ''dimple'' crossed dipolar trap. The collisional processes between atoms which are trapped in a reservoir load in a non adiabatic way the dimple. The reservoir trap can be provided either by a dark SPOT Magneto Optical Trap, the (aberrated) laser beam itself or by a quadrupolar or quadratic magnetic trap. Optimal parameters for the dimple are derived from thermodynamical equations and from loading time, including possible inelastic and Majorana losses. We suggest to load at relatively high temperature a tight optical trap. Simple evaporative cooling equations, taking into account gravity, the possible occurrence of hydrodynamical regime, Feshbach resonance processes and three body recombination events are given. To have an efficient evaporation the elastic collisional rate (in s$^{-1}$) is found to be on the order of the trapping frequency and lower than one hundred times the temperature in micro-Kelvin. Bose Einstein condensates with more than $10^7$ atoms should be obtained in much less than one second starting from an usual MOT setup.Comment: 14 page

Non-Holonomic Control III : Coherence Protection by the Quantum Zeno Effect and Non-Holonomic Control

In this paper, we present a coherence protection method based upon a multidimensional generalization of the Quantum Zeno Effect, as well as ideas from the coding theory. The non-holonomic control technique is employed as a physical tool which allows its effective implementation. The two limiting cases of small and large quantum systems are considered

Non-Holonomic Control IV : Coherence Protection in a Rubidium isotope

In this paper, we present a realistic application of the coherence protection method proposed in the previous article. A qubit of information encoded on the two spin states of a Rubidium isotope is protected from the action of electric and magnetic fields

Non-Holonomic Control I

In this paper, we present a universal control technique, the non-holonomic control, which allows us to impose any arbitrarily prescribed unitary evolution to any quantum system through the alternate application of two well-chosen perturbations

Observation of a resonant four-body interaction in cold cesium Rydberg atoms

Cold Rydberg atoms subject to long-range dipole-dipole interactions represent a particularly interesting system for exploring few-body interactions and probing the transition from 2-body physics to the many-body regime. In this work we report the direct observation of a resonant 4-body Rydberg interaction. We exploit the occurrence of an accidental quasi-coincidence of a 2-body and a 4-body resonant Stark-tuned Forster process in cesium to observe a resonant energy transfer requiring the simultaneous interaction of at least four neighboring atoms. These results are relevant for the implementation of quantum gates with Rydberg atoms and for further studies of many-body physics.Comment: 5 pages, 5 figure

Constraint on the time variation of the fine-structure constant with the SDSS-III/BOSS DR12 quasar sample

From the Sloan Digital Sky Survey (SDSS) Data Release 12, which covers the full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate the possible variation of the fine-structure constant over cosmological time-scales. We analyse the largest quasar sample considered so far in the literature, which contains 13175 spectra (10363 from SDSS-III/BOSS DR12 + 2812 from SDSS-II DR7) with redshift $z<\,$1. We apply the emission-line method on the [O III] doublet (4960, 5008 A) and obtain $\Delta\alpha/\alpha= \left(0.9 \pm 1.8\right)\times10^{-5}$ for the relative variation of the fine-structure constant. We also investigate the possible sources of systematics: misidentification of the lines, sky OH lines, H$\,\beta$ and broad line contamination, Gaussian and Voigt fitting profiles, optimal wavelength range for the Gaussian fits, chosen polynomial order for the continuum spectrum, signal-to-noise ratio and good quality of the fits. The uncertainty of the measurement is dominated by the sky subtraction. The results presented in this work, being systematics limited, have sufficient statistics to constrain robustly the variation of the fine-structure constant in redshift bins ($\Delta z\approx$ 0.06) over the last 7.9 Gyr. In addition, we study the [Ne III] doublet (3870, 3969 A) present in 462 quasar spectra and discuss the systematic effects on using these emission lines to constrain the fine-structure constant variation. Better constraints on $\Delta\alpha/\alpha\$ ($<$10$^{-6}$) using the emission-line method would be possible with high-resolution spectroscopy and large galaxy/qso surveys.Comment: 16 pages, 16 figures. Version published in MNRAS. Analysis enlarged, public catalogue now availabl

Coherent excitation of a single atom to a Rydberg state

We present the coherent excitation of a single Rubidium atom to the Rydberg state (58d3/2) using a two-photon transition. The experimental setup is described in detail, as well as experimental techniques and procedures. The coherence of the excitation is revealed by observing Rabi oscillations between ground and Rydberg states of the atom. We analyze the observed oscillations in detail and compare them to numerical simulations which include imperfections of our experimental system. Strategies for future improvements on the coherent manipulation of a single atom in our settings are given

Entanglement of two individual atoms using the Rydberg blockade

We report on our recent progress on the manipulation of single rubidium atoms trapped in optical tweezers and the generation of entanglement between two atoms, each individually trapped in neighboring tweezers. To create an entangled state of two atoms in their ground states, we make use of the Rydberg blockade mechanism. The degree of entanglement is measured using global rotations of the internal states of both atoms. Such internal state rotations on a single atom are demonstrated with a high fidelity.Comment: Proceeding of the 19th International Conference on Laser Spectroscopy ICOLS 2009, 7-13 June 2009, Hokkaido, Japa