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

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)

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

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

6Li 3D-MOT

– Number of atoms: ~ 2.2 · 108 at.

– Loading time: ~ 5s

– Lifetime,

6Li MOT size : 3mm21/04/23 12

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

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

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)

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)

back

What is the ground state of a mixture of strongly interacting Fermi gases with large mass difference ?

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