KRb degenerate mixtures with tunable interactions

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K-Rb degenerate mixtures with tunable interactions
Giacomo Roati LENS, University of
Florence, and INFM-CNR
ESF QUDEDIS
workshop
"BEC in Poland
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People involved
Chiara DErrico
Michele Modugno
Matteo Zaccanti
Mattia Jona-Lasinio
Andrea Simoni (Rennes)
Marco Fattori
Prof. Giovanni Modugno
Giacomo Roati
Prof. Massimo Inguscio
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Tuning the interactions ?

• Controlling mean-field energy
• Collapse and phase-separation
• An ideal Bose-Einstein condensate

• High correlated systems
• BCS-BEC crossover
• BCS-like transition in fermionic systems

• Producing ultracold heteronuclear molecules
• Ground state molecules
• Long range dipole-dipole interactions

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Tuning the interactions ?
When a collisional channel of two atoms has the
same energy of a molecular state -gt Feshbach
resonance
Feshbach spectroscopy determination of the
collisional parameters
Tuning the interactions -gt tuning scattering
length a by means of an external homogeneous
magnetic field
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Outline (I)

• Introducing our systems K-Rb mixtures
• 40K-87Rb degenerate mixture
• Feshbach analysis collisional properties
• Tuning the interactions collapse and
  phase-separation
• Observation of heteronuclear K-Rb molecules

• 39K-87Rb degenerate mixture
• Feshbach analysis collisional properties
• 39K Bose-Einstein condensate with tunable
  interactions
• Bloch oscillations

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K-Rb degenerate mixtures

• Potassium is interesting in the frame of
  degenerate quantum gases
• two bosonic (39K and 41K ) and one fermionic
  (40K) isotopes.

• 39K, 41K cannot be brought to BEC by standard
  evaporation techniques
• laser cooling to low temperatures and high
  densities is prevented.

• 40K is a fermion

no s-wave for identical fermions and p-wave is
suppressed _at_ ultracold temperature (lt 50 ?K) no
direct evaporative cooling

• The idea

Sympathetic cooling with 87Rb.
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Sympathetic cooling
KRb evaporate directly only rubidium elastic
collisions cool potassium
G. Modugno, G. Ferrari, G. Roati, R. Brecha, A.
Simoni, and M. Inguscio Science 294, 1320 (2001)
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41K Bose-Einstein condensate
G. Modugno et al.Science 294, 1320 (2001) G.
Modugno, et al. PRL, 89, 190404 (2002)
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41K-87Rb Bose-Bose mixtures _at_ LENS
Jacopo Catani Luigi De Sarlo Giovanni
Barontini Francesco Minardi
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Bose-Bose mixtures in a 3D lattice
Shift in the superfluid to Mott insulator
transition when K BEC is added
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40K-87Rb degenerate mixtures
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40K-87Rb degenerate mixture
NF, NB 104-105
Numbers Temperatures
lt 0.5 TC 0.3 TF
Spin-polarized fermions no collisions Spin
mixtures of fermions, bosons or mixtures of
bosons and fermions adjustable collisions

G. Roati et al PRL 89, 150403 (2002)
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Feshbach spectroscopy
Ferlaino et al, Phys. Rev. A 73, 040702(R) (2006)
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Feshbach spectroscopy
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Feshbach spectroscopy

• The quantum collisional model can be used to
• determine the position and width of all
  Feshbach resonance for the
• K-Rb isotopic pairs
• determine the scattering lengths for the other
  isotopic pairs (Bose-Bose mixtures with 41K-87Rb
  and 39K-87Rb)

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B0 546.65 (20) G
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Collapse and phase-separation
Rb BEC
B0 546.65 (20) G
Zaccanti et al, Phys. Rev. A 74, 041605(R) (2006)
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Molecules

• 30-40 maximum conversion efficiency
• Lifetime of the molecules seems short tlt0.1 ms
  (also at JILA, D. S. Jin et al.) -gt
  atom-molecule collisions (unpaired atoms must be
  removed)
• Tight optical lattices can be used to reduce the
  losses (t100ms observed in Hamburg (K. Bongs et
  al.)

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Perspectives

• Production of molecules is possible, but requires
  stabilization in optical lattices.

Raman scheme to bring the molecules to ground
state permanent electric dipole
d 1 Debye
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39K-87Rb degenerate mixtures
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General
motivations

• Bose-Einstein condensate
• Macroscopic occupation of a single quantum
  state bright source of atoms
• Very narrow momentum distribution monochromatic
  source of atoms
• Coherent matter wave -gt BEC Laser?
• BEC ideal system for high precision
  interferometry?

Interactions -gt BEC
Interactions -gt decoherence in trapped systems
-gt mean-field instability in optical lattice
-gt short-living Bloch oscillations with trapped
BEC
L.De Sarlo et al. PRA 72, 013603 (2005) B.P.
Anderson and M. Kasevich, Proceedings of the
International School of Physics Enrico Fermi
Course CXL, edited by M. Inguscio, S. Stringari
and C. Wieman , IOS Press Amsterdam (1999).
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General
motivations

• Bose-Einstein condensate
• Macroscopic occupation of a single quantum
  state bright source of atoms
• Very narrow momentum distribution monochromatic
  source of atoms
• Coherent matter wave -gt BEC Laser?
• BEC ideal system for high precision
  interferometry?

Interactions -gt BEC
Interactions -gt decoherence in trapped systems
-gt mean-field instability in optical lattice
-gt short-living Bloch oscillations no spatially
high resolution interferometry
-gt hiding physics in disordered potentials
(Chiara Forts talk)
T.Shulte et al. PRL 95 170411 (2005) J .Lye et
al. cond-mat/0611146v1 (2006)
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General
motivations

• Bose-Einstein condensate and Feshbach resonances
  
• -gt tunable interactions (agt0 lt-gtalt0)
• Weak interactions regime in a BEC
• BEC with zero scattering length -gt physics _at_
  micrometer scale

a lt 0 -gt Still unexplored physics -gt Quantum
physics Schrodinger cats in double well
potential
a 0 -gt Bloch oscillations with high spatial
resolution interferometry -gt Disordered systems
Anderson-like transition
L. Khaykovich et al. Science 296, 1990 (2002)
K.E. Strecker et al. Nature 417, 150 (2002)
T.Weber et al. Science 299, 232 (2003)
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Outline (II)
K-K and K-Rb Feshbach resonances
39K Bose-Einstein condensate with tunable
interactions
Tuning the interactions weak interacting regime
39K BEC in a vertical optical lattice Bloch
oscillations
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Cooling potassium
Unfavorable collisional properties and negative
scattering length no 39K BEC!
aKK-33 a0
Predicted K-K broad Feshbach resonances BEC with
tunable interactions!
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How cooling
potassium
Sympathetic cooling with Rb in the magnetic trap
is efficient (aKRb28 a0) , but BEC is prevented
by the K-K negative scattering length.
Predicted K-Rb Feshbach resonances sympathetic
cooling in optical potentials
L.De Sarlo et al. PRA 75, 022715 (2007)
F.Ferlaino et al. PRA 73, 040702 (2006)
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39K-87Rb mixture in optical trap
We load the mixture in a crossed optical trap _at_
1033 nm and we transfer the atoms in the absolute
ground state F1, mF1.
rubidium
potassium
?Rb 2?? 110 Hz ?K 2?? 160 Hz
NRb ? 1? 106 and NK ? 3.5?105 atoms _at_1.8 ?K
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Feshbach
resonances
Several broad Feshbach resonances
Improving the collisional models
aKK -33.3 (3) a0
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39K Bose-Einstein
condensate
12 G. Roati et al. cond-mat 0703714 (2007)
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Tuning the
interactions

• B gt 398.5 G -gt 3-body losses due to Feshabach
  resonance K3?a4
• 350.2 G ltBlt398.5 G -gt stable BEC with tunable
  positive interactions
• B lt 350.2 G -gt BEC with negative interactions
• Stable BEC with negative interactions (N,a)
• Collapse ac aho/ N

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Adiabatically tuning to the weak interacting
regime _at_ 350 G.
decreasing a
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Probing the tunability of interactions
expansion of the BEC vs magnetic field
aK0 -gt ground state of the harmonic oscillator,
Erel pure kinetic energy
aK?0 -gt Erelkinetic enery internal energy
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Comparison of the experimental data with GPE (M.
Modugno). a(B) taken from our quantum
collisional model.
BthZC 350.4 (4) Gauss
athColl -0.57 (20) a0
aexpColl -0.2 (3) a0
Control of a to zero within 0.05 a0 !
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39K BEC in optical lattice with tunable
interactions
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Quantum interference of Wannier-Stark states
Bloch oscillations
Interferometry Spatial resolution -gt size of
the sample Sensitivity -gt momentum distribution
Interactions decoherence -gt BEC thermal
sample
Thermal systems -gt long living BO (????? a) Size
of the sample -gt limited by T
Ideal Bose-Einstein condensate ?
G.Roati et al. PRL 92, 230402 (2004) G. Ferrari
et al. PRL 97, 060402 (2006)
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Bloch oscillations

• N4?104 atoms
• ?1033 nm
• s5
• ?rad 50 Hz

The spatial extent of the cloud typical
parameters (s,?) scattering length a0 -gt
harmonic oscillator ground state
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ms
5.6 5.8 6
7 451 451.5
452 452.5 453
TB2.2 ms
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Conclusions and Perspectives

• 39K BEC with tunable interactions new system
• High spatial resolution interferometry with
  trapped BEC
• Quantum physics with attractive interacting BEC
• Ideal BEC and disordered potentials Anderson
  localization?