Transcript (Ultra-)Cold Molecules (Ultra

(Ultra-)Cold Molecules
What difference does
a (micro-)Kelvin make?
Olivier Dulieu
Laboratoire Aimé Cotton, CNRS, Campus d’Orsay, Orsay, France
[email protected]
(Ultra-)Cold Molecules
What difference does
a (micro-)Kelvin make?
Olivier Dulieu
Laboratoire Aimé Cotton, CNRS, Campus d’Orsay, Orsay, France
[email protected]
Molecules are really cool!
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« The subtle flirtation of ultracold atoms »,Science, 280, 200 (1998): « If highenergy accelarators make the rap music of physics-with their whirling particles
and rapid-free smashups, then collisions between ultracold atoms are its
Wagnerian opera »
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« 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. »
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« Hot prospects for ultracold molecules », B. Goss Levi, Physics Today, Sept.
2000, p.46
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« 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.
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« Really cool molecules », P. S. Julienne, Nature, 424, 24 (2003)
(Envisioned?) Applications of cold molecules
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Ultra-high resolution spectroscopy
Test of fundamental theories
Superchemistry
Ultracold Photochemistry
Quantum properties, BCS, superfluidity
Ultimate control of reactive collisions
Quantum information
Biology…
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Ultra-high resolution spectroscopy (1)
Accurate determination of the van der Waals coefficient in Cesium
100 highlying levels
 C6 / R 6
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 …

N (t )  N avg  t  A exp(  t ) sin 2  02   2 4 2

Test of fundamental theories:
Electron dipole moment with heavy polar molecules
Effective electric field seen by the valence electron:
e
eff=
QP
structure
Degree of polarization due to an
external field; moderate for a polar
molecule
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 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
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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 COMOL
HPRN-CT-2002-00290
São Pedro 2004
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Heidelberg 2002
Les Houches 2002
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Boulder 1997
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Telluride 1994
Lago di Como 1989
http://www.lac.u-psud.fr/coldmolecules
Outline of this week’ lectures
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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!
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…
• Another solution: photoassociation of cold atoms…
Other theoretical approaches:
Optimal Control Theory
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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, CaH
DiRosa 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
Photoassociation of cold atoms+stabilization
• transfer density of
probability inwards,
• to produce deeply-bound
ultracold molecules
• See lecture on Thursday
Cs2: Orsay, PRL, 80, 4402 (1998);
Rb2: Pisa, PRL, 84, 2814 (2000)
Alternative methods for cooling molecules
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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
Weinstein et al, Nature 395, 148 (1998)
(J. Doyle@Harvard, A. Peters@Berlin)
Expansion out of a rotating nozzle
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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)
Phase space filtering (G. Rempe@Garching)
Billiard-like collisions
(D. Chandler@Sandia Labs)
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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)
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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 104 4He atom droplets
T=2.7K
Excitation spectra of the dimers
Toennies et al, Physics Today 54, p31 (2001)
Feshbach molecules