QUEST - Centre for Quantum Engineering and Space-Time Research

1

Institut für Quantenoptik, Leibniz Universität Hannover

D. Fim, A. Kulosa, S. Rühmann, K. Zipfel, W. Ertmer and E. Rasel

A continuous loading scheme for a dipole trap

QUEST - Centre for Quantum Engineering and Space-Time Research

2Dominika Fim – RTG 1729

A magnesium frequency standard

n(24Mg: 1S0 → 3P1 )= 655 659 923 839 730 (47) Hz

Limited by the doppler effet 1st order

TT

QUEST - Centre for Quantum Engineering and Space-Time Research

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Stability of clocks:

1st order Doppler broadening vanish improves with a higher number of

atoms

A magnesium frequency standard

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

4

• Optical cooling of magnesium– Stepwise loading scheme of dipole traps

• Limitations– Continuous loading scheme of dipole traps

• Comparison of the loading schemes• Improvements• Conclusion

Outline

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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Optical cooling of magnesiumSinglet Triplet

(3s2) 1S0

(3s3p) 1P1

012

(3s3p) 3P

231

(3s3d) 3D

383 nm26 MHz

457 nm36 Hz

285 nm78 MHz

5

Singlet-MOT: 3 mKSinglet-MOT: 3 mK Interkombination transition:low photon scattering rate

Singlet-MOT: 3 mK intercombination transition:low photon scattering rate

Triplet-MOT: 1 mKdensity limitation!

Light at the magic wavelength ionize atoms from 3D states

469 nm

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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Singlet Triplet

(3s2) 1S0

(3s3p) 1P1

012

(3s3p) 3P

231

(3s3d) 3D

285 nm78 MHz

Singlet-MOT:Number of atoms: 3 10∙ 9 Temperature: 3mK

S-MOT

Decay of the number of atoms:

R - loading rate = 5 10∙ 8 1/sα - one-body lossesƮ = 1/α 17s ̴Limitation: one-body loss

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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T-MOT

Singlet Triplet

(3s2) 1S0

(3s3p) 1P1

012

(3s3p) 3P

231

(3s3d) 3D

383 nm26 MHz

457 nm36 Hz

285 nm78 MHz

Triplet-MOT:Number of atoms: 10 ̴ 8 Temperature: 1mK

Decay of the number of atoms:

α - one-body lossesβ - two-body lossesƮ = 1/α ̴ 1 s (decay: 3P1 → 1S0 )Two-body loss at high number of atoms

Trap time tdec / s

Num

ber o

f ato

ms:

T-M

OT

Sequential loading scheme:

Atoms in the dipole trap: 3P2 state limited by binary collisions and density

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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Continuous- loading scheme

Singlet Triplet

(3s2) 1S0

(3s3p) 1P1

012

(3s3p) 3P

231

(3s3d) 3D

383 nm26 MHz

457 nm36 Hz

285 nm78 MHz

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

9

Comparison of the loading schemes

• Loading rates are equal: 1.2 10∙ 3 1/s • Continuous loading: limited by lifetime Ʈ = 4.5 s• Sequential: saturation at Ʈ = 1.1 s

capture time / s

Atom

zahl

Lifetime of the dipole trap

loading time / s

continuous τ=4,5 s

sequential τ=1,1 s

Atom

zahl

loading: dipole trap

Num

ber

of a

tom

s N

Num

ber

of a

tom

s N

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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• spatial expansion of the T-MOT (limited by temperature)

→ low detuning→ high intensity

→ Density limitation: high photon scattering rate (reabsorption, inelastic collisions)→ Optimization only for the continuous loading scheme

Enhancement of the loading rate

W0= 11 mmW0= 3.1 mm

Saturation on 3P2 → 3D3

Num

ber o

f ato

ms i

n th

e di

pole

trap

Higher loadingefficiency due to higher Intensity

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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•small number of atoms: exponential decay

• high number of atoms: loss attributed to binary collisions

Raise of Temperature → elastic collisions rather unlikely→ inelastische collisions

Decay curve

0 2 4 6 8 10 12 14 16102

103

104

105Decay

num

ber o

f ato

ms i

n th

e dip

ole tr

ap time / s

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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3P0 + 3P0

1S0 + 3P0

2,7 eVEner

gie

3P0 + 3P0

1S0 + 3P0

0,024 eV

(3s2)1S0 + (3s4s)1S0

2,7 eVEner

gie

Due to the collision both atoms change their atomic state→ for the low energy difference collision at high distances possible

Ʈ = 1/α = 4.2 s A high energy difference requires a low distance → rather unlikely

Singulett Triplett

(3s2) 1S0

(3s3p) 1P1

012

(3s3p) 3P

231

(3s3d) 3D(3s4s) 1S0

Inelastic collisions

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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Results

-> the dipole trap loading rate was increased by two orders of magnitude:

3 10∙ 5 atoms in the trap!!

Number of atoms:Stepwise: 1.1 10∙ 3 Continuous: 4.5 10∙ 3 Optimized continuous: 3 10∙ 5

Loading rate:Stepwise/Continuous: 1.2 103 1/sOptimized continuous: 1.3 105 1/s

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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...we were able to trap magnesium atoms in an optical lattice

Singulett Triplett

(3s2) 1S0

(3s3p) 1P1

012

(3s3p) 3P

231

(3s3d) 3D

383 nm26 MHz

457 nm36 Hz

285 nm78 MHz

10.000 Atome in 3 s !!

…due to the continuous loading scheme

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

1525.03.2010 15

• 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

Conclusion

Dominika Fim – RTG 1729

QUEST - Centre for Quantum Engineering and Space-Time Research

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Prof. Dr. Wolfgang Ertmer

Prof. Dr. Ernst M. Rasel

Group leader…

Dominika Fim – RTG 1729

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…and the magnesium Team