Towards sympathetic cooling of molecules with ultracold atoms

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Towards sympathetic cooling of molecules with
ultracold atoms
Adela Marian Fritz-Haber-Institut, Berlin
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Outline

• Introduction
• Slowing molecules using a wire
• Stark decelerator
• AC electric trapping of rubidium atoms

• Idea
• First results
• Outlook

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Sympathetic cooling of molecules by ultracold
atoms
Requirements
?

• The molecules need to be trapped in their
  lowest-energy quantum state.
• The trapped clouds of atoms and molecules need
  to be spatially overlapped.
• The atom and molecule traps should not perturb
  each other.

?
?
Our approach
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Principle of Stark deceleration
HV
LFS Molecule enters E-field
LFS Molecule exits E-field
-HV
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Principle of Stark deceleration
time 1
synchronous molecule flying through an array of
deceleration stages
kinetic energy loss at each stage
time 2
H. L. Bethlem et al., PRL 83, 1558 (1999)
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Most efficient Stark decelerator

• 85 cm long
• need 3 modules for best decelerated signal

L. Scharfenberg et al., PRA 79, 023401 (2009)
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Combining atom and molecule machines

• very different vacuum requirements

• molecules 10-8 mbar
• atoms 10-10 mbar

• spatial constraints

OR use special extension
use best big decelerator

• high-density beams
• too far away

• close to atom trap
• technically very difficult

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Idea mini-decelerator
101 compared to one of the big machines
6 mm electrodes 4 mm x 4 mm gap 20 000 V
applied voltage 1111 mm length 100 stages
gt 0.6 mm electrodes gt 0.4 mm x 0.4 mm gap gt
2000 V applied voltage gt 111 mm length gt 100
stages
Solution use Ø0.6 mm Ta wire
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Comparison with the big decelerators
Advantages

• short decelerator

• compact vacuum system
• good for short-lived molecules

• bakeable
• lower costs

• smaller vacuum chamber(s)
• smaller pumps
• cheap electrodes
• lower voltage supplies and switches

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Comparison with the big decelerators
Disadvantages

• very small gap gt less molecules accepted
• gt construction
  precision

• possible to obtain 0.01 mm accuracy!

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Experimental setup
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Recent data Deceleration of 13CO
2.0
1.5

• mean beam velocity 500 m/s
• pressure in decelerator chamber
• (with gas load) 6 x 10-9 mbar

Intensity (arb. units)
1.0

• applied voltage 2 kV
• decelerated peak 450 m/s

0.5
0.0
1.2
1.1
1.0
0.9
0.8
0.7
0.6
Time of flight (ms)
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Recent data Deceleration of 13CO
3 kV applied voltage!
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Conclusion Outlook
We have decelerated CO molecules using a wire
decelerator.

• bake out decelerator 1st UHV-compatible
  decelerator
• condition to even higher voltages
• use a cooled valve to reduce initial velocities

Next steps

• Collisions experiments with trapped atoms

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Flying through the decelerator(A molecule's view)
Courtesy of Henrik Haak
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Thanks
Gerard Meijer Henrik Haak Peter Geng Sam Meek Bas
van de Meerakker
Thank you for your attention!
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Operation principle of an AC electric trap
A saddle point is created for the electric field
which can be rapidly switched around
J. van Veldhoven et al., PRL 94, 083001 (2005)
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Electric fields in the trap
z
r
r focusing
z focusing
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Frequency scan
x 10 5
2.5
Expt
Theory
2.0
1.5
Number of atoms
1.0
0.5
0.0
75
70
65
60
55
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Switching frequency (Hz)

• Taken after a trapping time of 5 s
• Frequency range agrees with trajectory
  calculations
• 2.5 x 105 atoms _at_ 61 Hz

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Dynamic confinement of the atoms
(a)
(c)
(b)
g
(e)
(d)
0.25
z
Optical density
r
0
focusing
r

• Pictures taken at a switching
• frequency of 60 Hz after 1 s
• of trapping
• Switching cycle asymmetric
• with 59 r focusing
• Excellent agreement with
• trajectory calculations

c
a
b
d
e
z focusing
T16.7 ms
Time
S. Schlunk et al., PRL 98, 223002 (2007)
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Mapping of the electric fields
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Acknowlegdment
Sophie Schlunk Wieland Schöllkopf Peter
Geng Amudha Duraisamy Gerard Meijer
Thank you for your attention!