Transcript Slide 1

Experiments with ultra-cold Fermion
Mixture: 40K - 6Li
Saptarishi Chaudhuri, Christophe Salomon, Frederic Chevy, David Wilkowski
Armin Ridinger, Thomas Salez, Ulrich Eismann
17/07/2015
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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
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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
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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
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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
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Schematic of the experiment
6Li- Zeeman
40K
slower
To be installed
2D+-MOT
Magnetic transport
high resolution
imaging
6Li-40K
double species
3D-MOT
Degenerate gas
in optical lattices
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Science
chamber
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2D+MOT
Li-oven
3D-MOT
Zeeman-slower
Magnetic transport
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Laser System: Potassium
• Single Master diode laser
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
• Convenient design to include Bosonic 39K
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The 2D+ MOT for
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40K
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40K
2D+ MOT
• 3D-MOT Loading rate: 2 x109 at./s
Mean velocity ≈ 20 m/s
Lifetime, 3 sec (two body), 17 sec (vac)
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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
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6Li
3D-MOT
– Number of atoms: ~ 2.2 · 108 at.
– Loading time: ~ 5s
– Lifetime,
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6Li
MOT size : 3mm
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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.
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Photo-association: 40K2 molecules
K(2S) + K (2P)
E
PA laser
K(2S) + K (2S)
R (inter-atomic)
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Photo-association: 40K2 molecules
PA beam (650 mW, 4.4 mm2)
MOT
Mirror
Photodiode
(+ amplifier)
Wavelengthmeter
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Slow scan (5 GHz/min)of PA laser frequency
(PA loss must compete with other loss mechanisms)
~ 10% contrast at molecular resonances
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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)
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Molecular transitions near dissociation
limit
PA laser scan upto
250 GHz
Identification of >40
Molecular transitions
Loss by production of
40K molecules
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Effect of light shift
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Energy of photoassociation lines
For V(R)= -C3/R3 long range potential (dipole-dipole),
the energy of high lying bound states scales as:
En   A(n  n0 )6
This is simply deduced from a WKB approx. near dissociation limit.
R. Le Roy and R. Bernstein,
J. Chem. Phys. 52, 1970
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.
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Very good agreement with
Wang et al. (PRA, 53, R1216)
value: 14.14 (5)
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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)
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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
Complete simulation in order to ensure:
Minimization of loss of atoms
during transport
Negligible heating of atoms
Transport length ~ 40 cm
Transport with elbow
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1s transport duration
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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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What is the ground state of a mixture of strongly interacting
Fermi gases with large mass difference ?
A Wigner Crystal !
D. Petrov, G Astrakharchik, D. Papoular, C. Salomon, G. Shlyapnikov, PRL 99 (2007)
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