Rovibrational cooling of molecules by optical pumping Experimental - PowerPoint PPT Presentation

Rovibrational cooling of molecules by optical pumping Experimental results for laser cooling of molecules Isam Manai isam.manai@u-psud.fr Laboratoire Aimé Cotton Orsay France Quantum Technologie Conference III Septembre 9-15, 2012

Cold Molecules: Why? n/cm 3 l DB ~ distance between particles 10 12 Quantum properties Bose-Einstein gaz Quantum information 10 9 Control of collisions small velocity Quantum chemistry Precision measurement l DB = h/mv ∝ T -1/2 (quantum size) ~ 10 6 Fundamental test classical size of particles (1nm) 10 -9 T/K 10 -6 10 -3 1 nK µK mK K

Precise/long measurement • Cold molecules  Slow molecules  long interaction time D t OH, CO, … radiative lifetime (50ms) PRL 95 013003 (2005) • D E ~h/ D t  precise measurement (atomic clock) ND3 hyperfine structure (Hz) EPJD 31 337349 (2004) Effect of black body radiation! G. Meijer (Berlin) , J. Ye (JILA), …

Fundamental test Variation of constant (10 3 better than atoms): PRL 99, 150801 (2007) * OH electronic level PRL 96 143004 (2006). Compare fine-structure with astrophysical data Da/a < 10 -16 /year * Variation of m e /m p or constant α in spectra. Conincidence vibration and fine structure levels * Electron dipole (d) moment YbF (Hinds), PbO (DeMille, Doyle),... Shift – d.E due to electric E field inside the molecule GV/cm Improved measurement of the shape of the electron: Nature 473, 493 (26 May 2011) • Chirality: BaF or HSiO D. DeMille et al. PRL 100, 023003 (2008)

Control of (Reactive) collisions: quantum chemistry • Reactions at zero temperature (Resonnance, Tunneling) • Collisions in fields. External field to control dynamic • Create cold atoms by photodissociation SO 2  SO + O EPJD 46, 463 (2008) • CH 3 F + Ca +  CaF + + CH3 T. Sofltey PRL 100, 043203 (2008) • J. Ye, G. Meijer, G. Rempe, J. Doyle, M. Köln, H. Lewandowski … • macromolécules (perfluorinated) M. Arndt • Ions : M. Drewsen, S. Schiller, R.Wester , …

Outline 1)Photoassociation and cold molecules 2)Rovibrational Cooling of Cesium molecules by Optical pumping 3) Conclusion

Photoassociation Energy Photoassociation 6s+6p 3/2 (1) 1/R 3 Absorption of one photon by two cold atoms (T~100mK) (1) (2') (2'') Desexcitation Hot atoms (2') 6s 1/2 +6s 1/2 k B T 1/R 6 (2'') Cold molecules R Molecules in several vibrational levels 25 50 75 100 125 Internuclear distance

Experimental Setup Cs - MOT ~ 5 . 10 7 atoms ~10 11 at/cm 3 ~100µK - PA: Ti:Sa continu, 852 nm, ~1W Detection laser PA laser - Detection (ionization): pulsed laser 10 Hz-7ns, 5-10mJ/pulse - Optical pumping: femtoseconde laser, 12.5 ns, 770 nm, 1W

Population after Photoassociation PA Détection t (ms) 20 40 49 50 30000 Cs+ 2 25000 90 Laser d'ionisation 80 20000 70 Energie ( cm -1 ) C   u B  u 15000 60 50 10000 Cs+ 2 Em. Spon 40 v X = 0  v C = 0 v X = 0  v C = 1 PA 30 5000 20 V X 0 10 X   + 6s+ g 0 -5000 5 10 15 20 25 30 15900 15920 15940 15960 15980 16000 -1 ) R ( a 0 ) Fréquence de détection (cm

Need: Vibrational cooling Optical Pumping using shaped broadband laser 9600 1  u B 9500 9400 9300 -1 ) 1 2 3 i Energy (cm 9200 -3200 -3300 -3400 -3500 1  + X -3600 v=0 v=0 v=0 g 8 9 10 8 9 10 8 9 10 8 9 10 R (A 0 ) R (A 0 ) R (A 0 ) R (A 0 ) 140 120 Intensité 100 80 60 40 20 0 12800 12900 13000 13100 -1 ) nombre d'onde (cm Science 321, 232 (2008)

Population after pumping  Optical pumping PA opt. pump Detection  Efficiency ~ 65 % t (ms) 20 40 49 50 30000 Cs+ 2 25000 Laser d'ionisation 90 90 vX-vC = 0-2 0-1 0-0 80 80 20000 70 70 Energie ( cm -1 ) C   u B  u 15000 60 60 50 50 10000 Cs+ 2 Em. Spon 40 40 PA 30 30 5000 Femto 20 20 V X 0 X   + 10 10 6s+ g 0 0 -5000 5 10 15 20 25 30 15900 15900 15920 15920 15940 15940 15960 15960 15980 15980 16000 16000 R ( a 0 ) -1 ) Fréquence de détection (cm

Pumping to the dark v=1 Intensity (Arb) NJP 11 055037 (2009) Intensity (Arb) 0.8 Simulation 0.4 0.0 X Energy X X 0.8 Experiment 0.4 V=1 dark 0.0 12750 12900 13050 13200 Other v Wavenumber ( cm-1 ) coupled Internuclear distance

Better amplitude shaping Liquid Crystal spatial light modulator (SLM) 640 pixel 0.06nm resolution ~ 1 cm -1 Collaboration with Béatrice Chatel, Laboratoire Collision Agrégat Réactivité, Toulouse

Pumping to a chosen dark state ! V=0 dark a) 3% 0-0 0-1 Intensity (Arb) 40 NJP 11 055037 (2009) 0.8 off/on 30 ratio + Cs 2 0.4 20 10 0.0 0 12600 12800 13000 13200 15920 15960 16000 b) Intensity (Arb) 40 1-0 1-1 1-2 1-3 0.8 X Energy V=1 30 X + Cs 2 X 0.4 20 10 0.0 V=2 dark 0 12600 12800 13000 13200 c) 15920 15960 16000 40 Intensity (Arb) 2-1 2-2 2-3 2-4 0.8 V=2 30 Other v + Cs 2 20 coupled 0.4 10 0.0 0 12600 12800 13000 13200 15920 15960 16000 d) Intensity (Arb) 60 7-8 7-9 7-10 7-11 Internuclear distance 0.8 V=7 Cs 2 + 40 0.4 20 Efficiency ~ 60% with SLM 0.0 0 15920 15960 16000 12600 12800 13000 13200 Wavenumber (cm -1 ) Wavenumber (cm -1 )

Population after pumping  Optical pumping PA opt. pump Detection  Efficiency ~ 65 % t (ms) 20 40 49 50 In one vibrational level many rotational levels are populated 30000 Cs+ 2 25000 Laser d'ionisation 90 90 vX-vC = 0-2 0-1 0-0 80 80 20000 70 70 Energie ( cm -1 ) C   u B  u 15000 60 60 50 50 10000 Cs+ 2 Em. Spon 40 40 PA 30 30 5000 Femto 20 20 V X 0 X   + 10 10 6s+ g 0 0 -5000 5 10 15 20 25 30 15900 15900 15920 15920 15940 15940 15960 15960 15980 15980 16000 16000 R ( a 0 ) -1 ) Fréquence de détection (cm

Detection of the rotation v C =1 1  u C J C = 4 3 2 1 v C =0  Detection: • For one vibrational level many rotational levels v X =1 are populated • Rotational separation (~600MHz)  Unresolved with the REMPI detection (3 GHz) 1  + X g J X = 3 2 1 0 v X =0

Detection of the rotation  Detection: • For one vibrational level many rotational levels are populated • Rotational separation (~600MHz) Pulsed laser  Unresolved with the REMPI detection (3 GHz) J B = 4  Detection with a narrowband laser 3 2  Desexcitation to many vibrational levels 1  REMPI detection in v X = 7 v B =3 Diode de détection R(0) Q(2) R(2) v X =7 20 + Number P(2) Q(4) R(4) P(4) 16 12 Cs 2 J X = 4 3 2 8 1 0 13141.75 13141.80 13141.85 13141.90 13141.95 13142.00 v X =0 -1 ] Wavenumber [cm

Selection rules : Δ J = 0, ±1 +  - 2) Rotational cooling a – P : J decrease by 1 in absorption modifies the vibration – Q : J constant  vib. cooling needed – R : J increase by 1 in absorption In practice: Too cool the rotation we use Cs 2 rotational structure excite the P branch too small to be shaped with grating R(0) R(2) Q(2) 20 + Number Q(4) P(2) R(4) P(4) 16 12 Cs 2 8 13141.75 13141.80 13141.85 13141.90 13141.95 13142.00 Wavenumber [cm -1 ] Only Even rotational distribution are populated The rotational states have a (+/-) parity given by the sign of (-1) J’+1 in 0 g - and (-1) J in 1 X∑ g

Rotational cooling Selection rules : Δ J = 0, ±1 +  - – P : J decrease by 1 in absorption – Q : J constant – R : J increase by 1 in absorption V= 0 , J = 0

The green spectrum : only odd rotational levels are populated The black one : only even rotational levels are populated The rotational states have a (+/-) parity given by the sign of (-1) J’+1 in 0 g - and (-1) J in 1 X∑ g Q(3) 16 R(3) R(1) 14 nbre d'ions P(5) 12 P(3) Q(5) Q(1) 10 8 13.14200x10 3 13.14180 13.14185 13.14190 13.14195 fréquences [cm-1] R(0) Q(2) R(2) 20 + Number P(2) Q(4) P(4) R(4) 16 12 Cs 2 8 13141.75 13141.80 13141.85 13141.90 13141.95 13142.00 Wavenumber [cm -1 ]

V= 0 , J = 1 V= 0 , J = 4

Conclusion - Accumulation of molecules in a choosen vibrational level using a shaped broadband femtoseconde laser New Journal of Physics, 11(5)(2009) Journal of Modern Optics, 56:2089-2099,(2009). Molecular Physics, 108 :795{810, (2010) Our vibrational cooling method is genaral method and can be used in any molecules, demonstrated recently in Bigelow group for NaCs molecules Optics Express, Vol. 20, No. 14, (2012)

Conclusion - Rovibrational cooling of Cs 2 molecules are also demonstrate Accepted in PRL V= 0 , J = 0 Transfert of molecules in a choosen rotational level V= 0 , J = 1 V= 0 , J = 4

Perspectives * With rovibrational cooling collision between molecules and atoms can be studied. * The method of rovibrational cooling could be extended to other molecules and molecular beams. * And also opens up general perspectives in laser cooling the external degrees of freedom of molecules.

Visitors  Marin Pichler  Maria Allegrini  Goran Pichler  Emiliya Dimova  Lirong Wang Theory LAC  Nadia Bouloufa  Olivier Dulieu Experiment LAC Thank you for your attention !  Isam Manai Collaboration  Ridha Horchani  Mehdi Hamamda  Béatrice Chatel  Sébastien Weber  Daniel Comparat (LCAM, Toulouse, France)  Hans Lignier  Pierre Pillet