Experiments with ultra-cold Fermion Mixture: 40 K - 6 Li Saptarishi Chaudhuri , Christophe Salomon, Frederic Chevy, David Wilkowski Armin Ridinger, Thomas Salez, Ulrich Eismann 17/06/22 1
Jan 22, 2016
Experiments with ultra-cold Fermion Mixture: 40K - 6Li
Saptarishi Chaudhuri, Christophe Salomon, Frederic Chevy, David Wilkowski
Armin Ridinger, Thomas Salez, Ulrich Eismann
21/04/23 1
Collaboration:
21/04/23 2
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)
21/04/23 3
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)
21/04/23 4
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
21/04/23 5
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
21/04/23 6
Zeeman-slower
Li-oven
3D-MOT
2D+MOT
Magnetic transport
21/04/23 7
Laser System: Potassium• Single Master diode laser
• Convenient design to include Bosonic 39K
21/04/23 8
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
21/04/23 9
40K 2D+ MOT
Mean velocity ≈ 20 m/s
Lifetime, 3 sec (two body), 17 sec (vac)
• 3D-MOT Loading rate: 2 x109 at./s
21/04/23 10
Laser System: Lithium• Single Master laser
21/04/23 11
• 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
21/04/23 13
Double MOT6Li: 5 x 108 atoms loaded in 5 s.40K: 1.5 x109 atoms loaded in 5 s.
21/04/23 14
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
21/04/23 16
Molecular transitions near dissociation limit
Loss by production of
40K2 molecules
Effect of light shift
PA laser scan upto250 GHz
Identification of >40Molecular transitions
21/04/23 17
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
21/04/23 18
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))
21/04/23 19
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
21/04/23 20
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:
21/04/23 21
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
21/04/23 22
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 ?
21/04/23 23