Experiments with ultra-cold Fermion Mixture: 40 K - 6 Li
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Transcript of Experiments with ultra-cold Fermion Mixture: 40 K - 6 Li
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Experiments with ultra-cold Fermion Mixture: 40K - 6Li
Saptarishi Chaudhuri, Christophe Salomon, Frederic Chevy, David Wilkowski
Armin Ridinger, Thomas Salez, Ulrich Eismann
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Collaboration:
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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
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Plan
2D+MOT: an efficient source of 40K atoms
6Li-40K double MOT
Introduction
Recent Photo-association experiments
Summary and outlook
Ongoing technical developments: New solid-state laser (for laser-cooling of Li, with F. Garbier) and Magnetic transport (Munich style)
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Motivation
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)
Ground state in harmonic trap in the limit of largemass imbalance: Wigner crystal
Quantum simulator in Optical lattices
Different trap depth in Optical traps (FORT and lattice) for different species
Investigation of physics at lower dimensions -> possibility of simulating large number of condensed matter phenomena including high Tc superconductivity
(spin) imbalanced Fermi gas (N. Navon talk; MIT, Rice. ENS)
Stable Fermi-Fermi mixture (F. Shreck talk, Walraven group talk)
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Few body physics (D. Petrov talk)
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Strategy of the experiment at ENS
Large number of atoms
High resolution imaging
Plugged Quadrupole trap
Magnetic transport to science cell with better vacuum and optical access
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Schematic of the experiment
40K 2D+-MOT
6Li- Zeeman slower
6Li-40K double species 3D-MOT
Science chamber
high resolution imaging
Magnetic transport
To be installed
Degenerate gasin optical lattices
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Zeeman-slower
Li-oven
3D-MOT
2D+MOT
Magnetic transport
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Laser System: Potassium• Single Master diode laser
• Convenient design to include Bosonic 39K
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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
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The 2D+ MOT for 40K
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40K 2D+ MOT
Mean velocity ≈ 20 m/s
Lifetime, 3 sec (two body), 17 sec (vac)
• 3D-MOT Loading rate: 2 x109 at./s
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Laser System: Lithium• Single Master laser
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• 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
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6Li 3D-MOT
– Number of atoms: ~ 2.2 · 108 at.
– Loading time: ~ 5s
– Lifetime,
6Li MOT size : 3mm21/04/23 12
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Double MOT of 40K and 6Li
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Double MOT6Li: 5 x 108 atoms loaded in 5 s.40K: 1.5 x109 atoms loaded in 5 s.
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Photo-association: 40K2 molecules
K(2S) + K (2S)
K(2S) + K (2P)
E
R (inter-atomic)
PA laser
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Photo-association: 40K2 molecules
MOT
Mirror
PA beam (650 mW, 4.4 mm2)
Wavelength-meter
Photodiode (+ amplifier)
Slow scan (5 GHz/min)of PA laser frequency(PA loss must compete with other loss mechanisms)
21/04/23 15~ 10% contrast at molecular resonances
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Overall shape of Fluorescence signal determined by :
1) MOT beam fluorescence
2) PA laser fluorescence
3) PA light shift, (which depends on detuning)
Photo-association signal close to dissociation limit
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Molecular transitions near dissociation limit
Loss by production of
40K2 molecules
Effect of light shift
PA laser scan upto250 GHz
Identification of >40Molecular transitions
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60( )nE A n n
R. Le Roy and R. Bernstein, J. Chem. Phys. 52, 1970
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.
A is related to C3 and to the exponentof long range potential
We find A/h= 0. 7067Giving C3= 14.13 (20) a.u.
Very good agreement withWang et al. (PRA, 53, R1216) value: 14.14 (5)
Energy of photoassociation lines
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Search for 6Li-40K Molecules
Challenge:
Small Franck-Condon factor (~ 3% compared to 40K2 lines)
Weak molecular transition strength, small loss coefficient -> difficult to detect
Solution:
Better S/N
Lock-in detection (ultraslow AM, 0.5 Hz !)(Already improvement by 1 order of magnitude in S/N)
Why interesting:
Polar molecule with high G.S. dipole moment (3.6 D)
Alternate way of precision determination of s-wave scattering length for40K-6Li scattering ( compare: E. Wille et. al., PRL, 100, 053201 (2008);Approach: S. Moal et. al. PRL, 96, 023203 (2006))
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Ref: wang et. al. J. chem phys., 108, 5767 (1998)
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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
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Magnetic Transport
• Why : better vacuum + optical access• How: Moving quadrupole trap by moving currents
1s transport duration
Transport with elbow
Transport length ~ 40 cm
Negligible heating of atoms
Minimization of loss of atomsduring transport
Complete simulation in order to ensure:
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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
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A Wigner Crystal !
D. Petrov, G Astrakharchik, D. Papoular, C. Salomon, G. Shlyapnikov, PRL 99 (2007)
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What is the ground state of a mixture of strongly interacting Fermi gases with large mass difference ?
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