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Experiments with ultra-cold Fermion Mixture: 40 K - 6 Li

Experiments with ultra-cold Fermion Mixture: 40 K - 6 Li. Saptarishi Chaudhuri , Christophe Salomon, Frederic Chevy, David Wilkowski Armin Ridinger , Thomas Salez , Ulrich Eismann. Collaboration:. Theory support: Y. castin, D. Petrov, G. Shlyapnikov , R. Combescot, I. Carusotto,

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Experiments with ultra-cold Fermion Mixture: 40 K - 6 Li

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  1. Experiments with ultra-cold Fermion Mixture: 40K - 6Li SaptarishiChaudhuri, Christophe Salomon, Frederic Chevy, David Wilkowski Armin Ridinger, Thomas Salez, Ulrich Eismann

  2. Collaboration: Theory support: Y. castin, D. Petrov, G. Shlyapnikov , R. Combescot, I. Carusotto, C. Lobo, S. Stringari, L. Dao, A. Georges, O. Parcollet, C. Kollath, J.S. Bernier, L. De Leo, M. Köhl New frequency doubled, all solid state Laser development (671 nm): F. Gerbier, ENS

  3. Plan • Introduction • 2D+MOT: an efficient source of 40K atoms • 6Li-40K double MOT • Recent Photo-association experiments • Ongoing technical developments: New solid-state • laser (for laser-cooling of Li, with F. Garbier) and Magnetic transport • (Munich style) • Summary and outlook

  4. Motivation • (spin) imbalanced Fermi gas (N. Navon talk; MIT, Rice. ENS) • Quantum simulator in Optical lattices Investigation of physics at lower dimensions -> possibility of simulating large number of condensed matter phenomena including high Tc superconductivity • Mass imbalance as an added degree of freedom (Munich, Innsbruck, • Amsterdam with 6Li-40K) • Heteronuclear molecules (K. Dieckmann’s talk, K-Rb system at JILA) • Stable Fermi-Fermi mixture (F. Shreck talk, Walraven group talk) • Few body physics (D. Petrov talk) • Ground state in harmonic trap in the limit of large • mass imbalance: Wigner crystal • Different trap depth in Optical traps (FORT and lattice) for different species

  5. Strategy of the experiment at ENS Large number of atoms Magnetic transport to science cell with better vacuum and optical access Plugged Quadrupole trap High resolution imaging

  6. Schematic of the experiment 6Li-Zeeman slower To be installed 40K 2D+-MOT Magnetic transport high resolution imaging 6Li-40K double species 3D-MOT Degenerate gas in optical lattices Science chamber

  7. Magnetic transport 2D+MOT Li-oven Zeeman-slower 3D-MOT

  8. Laser System: Potassium • Single Master diode laser • Convenient design to include Bosonic 39K 3x Tapered amplifier (Eagleyard): • PTA, max = 1.5 W @ 3 A & 20 mW injection • PTA, typ = 700 mW @ 1.8 A & 15 mW injection • P2D/3D = 230 mW (typ) after AOMs + fibers

  9. The 2D+ MOT for 40K

  10. 40K 2D+ MOT • Mean velocity ≈ 20 m/s Lifetime, 3 sec (two body), 17 sec (vac) • 3D-MOT Loading rate: 2 x109 at./s

  11. Laser System: Lithium • Single Master laser • 3x Tapered amplifier (Toptica): • PTA, max = 500 mW @ 960 mA & 15 mW injection • PZeeman = 120 mW after AOM + fibers • PMOT = 130 mW after AOMs + fibers

  12. 6Li 3D-MOT • Number of atoms: ~ 2.2 · 108 at. • Loading time: ~ 5s • Lifetime, 6Li MOT size : 3mm

  13. Double MOT of 40K and 6Li Double MOT 6Li: 5 x 108 atoms loaded in 5 s. 40K: 1.5 x109 atoms loaded in 5 s.

  14. Photo-association: 40K2 molecules K(2S) + K (2P) E PA laser K(2S) + K (2S) R (inter-atomic)

  15. Photo-association: 40K2 molecules PA beam (650 mW, 4.4 mm2) MOT Mirror Photodiode (+ amplifier) Wavelength-meter Slow scan (5 GHz/min)of PA laser frequency (PA loss must compete with other loss mechanisms) ~ 10% contrast at molecular resonances

  16. Photo-association signal close to dissociation limit Overall shape of Fluorescence signal determined by : 1) MOT beam fluorescence 2) PA laser fluorescence 3) PA light shift, (which depends on detuning)

  17. Molecular transitions near dissociation limit PA laser scan upto 250 GHz Identification of >40 Molecular transitions Loss by production of 40K2 molecules Effect of light shift

  18. A is related to C3 and to the exponent of long range potential We find A/h= 0. 7067 Giving C3= 14.13 (20) a.u. Very good agreement with Wang et al. (PRA, 53, R1216) value: 14.14 (5) Energy of photoassociation lines For V(R)= -C3/R3 long range potential (dipole-dipole), the energy of high lying bound states scales as: This is simply deduced from a WKB approx. near dissociation limit. R. Le Roy and R. Bernstein, J. Chem. Phys. 52, 1970

  19. Search for 6Li-40K Molecules Why interesting: Polar molecule with high G.S. dipole moment (3.6 D) Alternate way of precision determination of s-wave scattering length for 40K-6Li scattering ( compare: E. Wille et. al., PRL, 100, 053201 (2008); Approach: S. Moal et. al. PRL, 96, 023203 (2006)) Challenge: Small Franck-Condon factor (~ 3% compared to 40K2 lines) Weak molecular transition strength, small loss coefficient -> difficult to detect Ref: wang et. al. J. chem phys., 108, 5767 (1998) Solution: Better S/N Lock-in detection (ultraslow AM, 0.5 Hz !) (Already improvement by 1 order of magnitude in S/N)

  20. New all solid-state Laser (with F. Gerbier) All-new-solid-state Diode-pumped Single Mode 1342 nm Nd:YVO4 – laser External-cavity frequency doubling to 671 nm IR output target > 2W Efficient doubling > 80% should be feasible Output beam : TEM00

  21. Magnetic Transport • Why : better vacuum + optical access • How: Moving quadrupole trap by moving currents Complete simulation in order to ensure: Minimization of loss of atoms during transport Negligible heating of atoms Transport length ~ 40 cm Transport with elbow 1s transport duration

  22. Conclusion and Outlook • Development of a new experimental apparatus for ultra-cold and • quantum degenerate mixture of Fermionic atoms (40K-6Li). • Ongoing experiments on Photo-association: both homo-nuclear and • hetero-nuclear molecules • Next step: Magnetic transport and evaporation to Quantum degeneracy

  23. A Wigner Crystal ! D. Petrov, G Astrakharchik, D. Papoular, C. Salomon, G. Shlyapnikov, PRL 99 (2007) What is the ground state of a mixture of strongly interacting Fermi gases with large mass difference ? back

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