(Ultra-)Cold Molecules

(Ultra-)Cold Molecules What difference does a (micro-)Kelvin make? Olivier Dulieu Laboratoire Aimé Cotton, CNRS, Campus d’Orsay, Orsay, France olivier.dulieu@lac.u-psud.fr

Molecules are really cool! • « The subtle flirtation of ultracold atoms »,Science, 280, 200 (1998): « If high-energy accelarators make the rap music of physics-with their whirling particles and rapid-free smashups, then collisions between ultracold atoms are its Wagnerian opera » • « Molecules are cool », J. Doyle&B. Friedrich, Nature 401, 749 (1999): « Under ordinary conditions, atoms and molecules of a gas zigzag in all directions…[and] are most likely to move at the speed of riffle bullets… The emergence of methods for slowing and trapping gaseous species has lead to a renaissance in atomic physics, which is now progressing into molecular/chemical physics as well… Just as atom cooling is opening up new avenues of research, it is likely that the same will happen with molecular cooling – with repercussions for chemistry, and even, perhaps, in biology. » • « Hot prospects for ultracold molecules », B. Goss Levi, Physics Today, Sept. 2000, p.46 • « Quantum encounters of the cold kind », K. Burnett, P.D. Lett, E. Tiesinga, P.Julienne, C.J. Williams, Nature 416, 225 (2002) « We have already seen our dreams of controlling interactions on the quantum level come true, and the exquisite nature of this control has proved remarkable. These achievements have come from experimental and theoretical developments that have been a joy to be involved in, and their impact on new physics, chemistry and quantum computation has only just begun. • « Really cool molecules », P. S. Julienne, Nature, 424, 24 (2003)

(Envisioned?) Applications of cold molecules • Ultra-high resolution spectroscopy • Test of fundamental theories  • Superchemistry  • Ultracold Photochemistry  • Quantum properties, BCS, superfluidity • Ultimate control of reactive collisions • Quantum information • Biology… • …

Ultra-high resolution spectroscopy (1) Accurate determination of the van der Waals coefficient in Cesium 100 high-lying levels

Ultra-high resolution spectroscopy (2) Atomic radiative lifetime from molecular spectroscopy data

Ultra-high resolution spectroscopy (3) Accurate spectroscopy of a Feshbach resonance in 85Rb Using coherent atom-molecule oscillations in a BEC We precisely measured the binding energy of a molecular state near the Feshbach resonance in a 85Rb Bose-Einstein condensate. Rapid magnetic-field pulses induced coherent atom-molecule oscillations in the BEC. We measured the oscillation frequency as a function of B field and fit the data to a coupled-channel model. Our analysis constrained the Feshbach resonance position @155.041(18) G, width 10.71(2) G, and background scattering length 2443(3)a0 …

Test of fundamental theories: Electron dipole moment with heavy polar molecules Effective electric field seen by the valence electron: eeff=Q P Degree of polarization due to an external field; moderate for a polar molecule structure Interaction energy: V=-de. eeff

Quantum information p.067901

Superchemistry: they dreamed about it…. Phys. Rev.Lett. 84, 5029 (2000)

Superchemistry: they made it! Vol 417, p529 (2002)

BEC-BCS crossover

Cold and trapped molecular ions: toward complete control of chemical reactions? Atomic ions (from M. Drewsen, private communication)

Reaction MgH Reaction experiments 24Mg+(3p) + H2 -> 24MgH+ + H 26Mg+ Before reactions 24Mg+ 26Mg+ After reactions 24Mg+ 24MgH+ From M. Drewsen, private communication, and MOLEC XIV

Outline of this week’ lectures • 1- Introduction, overview • 2- Hamiltonian of a diatomic molecule • 3- Hund’s cases; Molecular symmetries • 4- Molecular spectroscopy • 5- Photoassociation of cold atoms • 6-Ultracold (elastic) collisions

References • H. Lefebvre-Brion&R.W. Field, « The Spectra and Dynamics of Diatomic Molecules », Elsevier Academic Press, 2004 • G. Herzberg, « The Spectra od Diatomic Molecules », Van Nostrand-Reinhold, Princeton, 1950, reprinted in 1989 by Krieger, Malabar. • Tutorials from G. Amat (Paris), A. Beswick (Orsay), C. Jungen (Orsay) • Bibliographic Databases: • DiRef: a bibliographic database for diatomic molecules, J. Mol. Spectrosc. 207, 287 (2001); http://diref.uwaterloo.ca • Cold Molecules: http://www.lac.u-psud.fr/coldmolecules, in progress

The Cold Molecule Network COMOLHPRN-CT-2002-00290 São Pedro 2004 … Heidelberg 2002 Les Houches 2002 … Boulder 1997 … Telluride 1994 Lago di Como 1989 http://www.lac.u-psud.fr/coldmolecules

Outline of this week’ lectures • 1-Introduction, overview • 2- Hamiltonian of a diatomic molecule • 3- Hund’s cases; Molecular symmetries • 4- Molecular spectroscopy • 5- Photoassociation of cold atoms • 6- Ultracold (elastic) collisions

Laser Cooling of Molecules…not so cool! • Another solution: photoassociation of cold atoms… A novel scheme is proposed for sequential cooling of rotation, translation, and vibration of molecules. More generally, this scheme manipulates and controls the states and energies of molecules. The scheme, while somewhat complex, is simpler and more feasible than simply providing a large number of synchronously but independently tunable lasers. The key component is a multiple single frequency laser in which a single narrow band pump laser generates an ensemble of resonant ‘‘stimulated Raman’’ sidebands subsequently amplified and selected in a sample of the molecules to be cooled….Only this specific order of rotation–translation–vibration appears feasible (using molecules produced by photoassociation of ultracold atoms avoids the requirement for translational cooling). Each step employs true dissipative cooling … by spontaneous emission and should yield a large translationally cold sample of molecules in the lowest v=0, J=0 level of the ground electronic state…

Other theoretical approaches:Optimal Control Theory • Thermodynamical analysis of the cooling of internal degrees of freedom: see A.Bartana & R.Kosloff, J. Chem. Phys 99, 196 (1993) • Numerical application (at LAC): C. Koch et al, Phys. Rev. A 70, 013402 (2004) « Stabilization of ultracold molecules using optimal control theory) Intermediate excited state Shaped pulse laser Initial (cold) molecule in high v Transfer to v=0

Direct laser cooling of BeH, CaHDiRosa et al@Los Alamos Rydberg transitions similar to the D1, D2 in alkali atoms (Nearly) Diagonal Franck-Condon matrices Good spectral isolation suitable for Doppler cooling Under progress

Cs2: Orsay, PRL, 80, 4402 (1998); Rb2: Pisa, PRL, 84, 2814 (2000) Photoassociation of cold atoms+stabilization • transfer density of probability inwards, • to produce deeply-bound ultracold molecules • See lecture on Thursday

Alternative methods for cooling molecules • Stark deceleration (2000) • Buffer gas cooling (1998) • Expansion out of a rotating nozzle (2004) • Phase space filtering (2004) • Billiard like collisions (2003) • Doped helium droplets (1992) • Feshbach resonances in a BEC (2003) • Reactive collisions (proposal in 1992)

Stark deceleration(G. Meijer@Berlin, E. Hinds@London) Bethlem et al, Nature 406, 491 (2000), Int. Rev. Phys. Chem. 22, 73 (2003)

Buffer gas cooling (J. Doyle@Harvard, A. Peters@Berlin) Weinstein et al, Nature 395, 148 (1998)

Expansion out of a rotating nozzle • M. Gupta & D. Hershbach, J. Phys.Chem A 105, 1626 (2001) • Zhao et al, Rev. Sci. Instr. 75, 146 (2004)

Phase space filtering (G. Rempe@Garching)

Billiard-like collisions (D. Chandler@Sandia Labs) • Elioff et al, Science 302, 1940 (2003)

Other techniques under progress (1)

Other techniques under progress (2)

Doped helium droplets (F. Stienckemeier@Bielefeld, G. Scoles@Princeton) • Mudrich et al, Eur. Phys. D (2004); Lewenrenz et al, J. Chem. Phys. 102, 8191 (1995) Pick up cell technique Na2 on the surface of 1044He atom droplets T=2.7K Excitation spectra of the dimers Toennies et al, Physics Today 54, p31 (2001)

Feshbach molecules

(Ultra-)Cold Molecules