QUEST - Centre for Quantum Engineering and Space-Time Research
A continuous loading scheme for a
dipole trap
Institut für Quantenoptik, Leibniz Universität Hannover
1
QUEST - Centre for Quantum Engineering and Space-Time Research
A magnesium frequency standard
n(24Mg: 1S0 → 3P1 )= 655 659 923 839 730 (47) Hz
T
T
Limited by the doppler effet 1st order
Dominika Fim – RTG 1729
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QUEST - Centre for Quantum Engineering and Space-Time Research
A magnesium frequency standard
Stability of clocks:
 1st order Doppler broadening
vanish
 improves with a higher number of
atoms
Dominika Fim – RTG 1729
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QUEST - Centre for Quantum Engineering and Space-Time Research
Outline
• Optical cooling of magnesium
– Stepwise loading scheme of dipole traps
• Limitations
– Continuous loading scheme of dipole traps
• Comparison of the loading schemes
• Improvements
• Conclusion
Dominika Fim – RTG 1729
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QUEST - Centre for Quantum Engineering and Space-Time Research
Optical cooling of magnesium
Singlet
Triplet
469 nm
1
3
2
(3s3d) 3D
(3s3p) 1P1
383 nm
26 MHz
285 nm
78 MHz
(3s2) 1S
0
2
1 (3s3p) 3P
0
457 nm
36 Hz
Singlet-MOT: 3mK
intercombination transition:
Interkombination
Light at
the magic wavelength ionize
low photon scattering
rate
3D states
atoms
from
Triplet-MOT: 1mK
density limitation!
Dominika Fim – RTG 1729
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QUEST - Centre for Quantum Engineering and Space-Time Research
S-MOT
Singlet-MOT:
Number of atoms: 3 ∙ 109
Temperature: 3mK
Decay of the number of atoms:
Singlet
1
3
2
(3s3d) 3D
108 1/s
R - loading rate = 5 ∙
α - one-body losses
Ʈ = 1/α ̴ 17s
Limitation: one-body loss
Triplet
(3s3p) 1P1
285 nm
78 MHz
2
1 (3s3p) 3P
0
(3s2) 1S0
Dominika Fim – RTG 1729
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QUEST - Centre for Quantum Engineering and Space-Time Research
T-MOT
Number of atoms: T-MOT
Triplet-MOT:
Number of atoms: ̴ 108
Temperature: 1mK
Decay of the number of atoms:
Sequential loading scheme:
Trap time
Atoms in the dipole trap: 3P2 state
limited by binary collisions and density
α - one-body losses
β - two-body losses
Ʈ = 1/α ̴ 1 s (decay: 3P1 → 1S0 )
Two-body loss at high number of
atoms
Singlet
tdec / s
Triplet
1
3
2
(3s3d) 3D
(3s3p) 1P1
383 nm
26 MHz
285 nm
78 MHz
2
1 (3s3p) 3P
0
(3s2) 1S0
Dominika Fim – RTG 1729
457 nm
36 Hz
7
QUEST - Centre for Quantum Engineering and Space-Time Research
Continuous- loading scheme
Triplet
Singlet
1
3
2
(3s3d) 3D
(3s3p) 1P1
383 nm
26 MHz
285 nm
78 MHz
(3s2) 1S
Dominika Fim – RTG 1729
0
2
1 (3s3p) 3P
0
457 nm
36 Hz
8
QUEST - Centre for Quantum Engineering and Space-Time Research
Comparison of the loading schemes
Lifetime of the dipole trap
continuous τ=4,5 s
sequential τ=1,1 s
of atoms N
Number
Atomzahl
Atomzahl
of atoms N
Number
loading: dipole trap
capture time / s
loading time / s
• Loading rates are equal: 1.2∙103 1/s
• Continuous loading: limited by lifetime Ʈ = 4.5 s
• Sequential: saturation at Ʈ = 1.1 s
Dominika Fim – RTG 1729
9
QUEST - Centre for Quantum Engineering and Space-Time Research
Enhancement of the loading rate
→ Density limitation: high photon scattering rate (reabsorption, inelastic collisions)
→ Optimization only for the continuous loading scheme
Higher loadingefficiency due to higher Intensity
• spatial expansion of the T-MOT
(limited by temperature)
→ low detuning
→ high intensity
Number of atoms in the dipole trap
W00= 3.1
mm
11 mm
Saturation on 3P2 → 3D3
Dominika Fim – RTG 1729
10
QUEST - Centre for Quantum Engineering and Space-Time Research
•small number of atoms:
exponential decay
• high number of atoms: loss
attributed to binary collisions
number of atoms in the dipole trap
Decay curve
Decay
5
10
4
10
3
10
2
10
0
2
4
6
8
10
12
14
16
time / s
Raise of Temperature
→ elastic collisions rather unlikely
→ inelastische collisions
Dominika Fim – RTG 1729
11
QUEST - Centre for Quantum Engineering and Space-Time Research
Inelastic collisions
Ʈ = 1/α = 4.2 s
A high energy difference
requires a low distance
→ rather unlikely
0,024 eV
(3s4s)
1S
0
Triplett
(3s3d) 3D
2,7 eV
1
3
2
Due to the collision both atoms
change
their atomic state
(3s3p) P
→ for the low energy12 difference
(3s3p) P
0
collision at high distances possible
1
+ 3P0
(3s2)1S0 + (3s4s)1S0
Energie
Singulett
3P
0
1
3
1S
0
+ 3P0
(3s2) 1S0
Dominika Fim – RTG 1729
12
QUEST - Centre for Quantum Engineering and Space-Time Research
Results
Number of atoms:
Stepwise:
Continuous:
Optimized continuous:
1.1 ∙ 103
4.5 ∙ 103
3 ∙105
Loading rate:
Stepwise/Continuous: 1.2 ∙ 103 1/s
Optimized continuous: 1.3 ∙ 105 1/s
-> the dipole trap loading rate was
increased by two orders of magnitude:
3 ∙ 105 atoms in the trap!!
Dominika Fim – RTG 1729
13
QUEST - Centre for Quantum Engineering and Space-Time Research
…due to the continuous loading
scheme
...we were able to trap magnesium atoms in an optical lattice
Singulett
Triplett
(3s3d) 3D
(3s3p) 1P1
285 nm
78 MHz
1
3
2
383 nm
26 MHz
2
1 (3s3p) 3P
0
457 nm
(3s2) 1S0 36 Hz
10.000 Atome in 3 s !!
Dominika Fim – RTG 1729
14
QUEST - Centre for Quantum Engineering and Space-Time Research
Conclusion
• Presented a continuous loading scheme for 3P0 which avoids density
limitation by introducing additional loss channel to T-MOT
• increased loading rate dipole trap by two orders of magnitude
• Number of atoms in the dipole trap is limited by two-body loss
collisions
25.03.2010
Dominika Fim – RTG 1729
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QUEST - Centre for Quantum Engineering and Space-Time Research
Group leader…
Prof. Dr. Wolfgang
Ertmer
Prof. Dr. Ernst
M. Rasel
Dominika Fim – RTG 1729
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QUEST - Centre for Quantum Engineering and Space-Time Research
…and the magnesium Team
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