Institut für Quantenoptik, Leibniz Universität Hannover

1. A continuous loading scheme for a dipole trap Institut für Quantenoptik, Leibniz Universität Hannover D. Fim, A. Kulosa, S. Rühmann, K. Zipfel, W. ErtmerandE. Rasel

2. A magnesium frequency standard n(24Mg: 1S0 → 3P1 )= 655 659 923 839 730 (47) Hz T T • Low sensitivity to blackbody radiation • Bosonic and fermionic isotopes available • Limited by the dopplereffet 1st order Dominika Fim – RTG 1729

3. A magnesium frequency standard Stability of clocks: • 1st order Doppler broadening vanish • improves with a higher number of atoms Dominika Fim – RTG 1729

4. 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

5. Optical cooling of magnesium Singlet Triplet 469 nm 1 (3s3d) 3D 3 2 383 nm 26 MHz (3s3p) 1P1 285 nm 78 MHz 2 1 (3s3p) 3P 0 457 nm 36 Hz (3s2) 1S0 Singlet-MOT: 3mK Light at the magic wavelength ionize atoms from 3D states Singlet-MOT: 3mK intercombinationtransition: lowphotonscattering rate Triplet-MOT: 1mK densitylimitation! Singlet-MOT: 3mK Interkombination transition: lowphotonscattering rate Dominika Fim – RTG 1729 5

6. S-MOT Decay of the number of atoms: R - loading rate = 5 ∙ 108 1/s α - one-body losses Ʈ = 1/α ̴ 17s Limitation: one-body loss Singlet Triplet Singlet-MOT: Number of atoms: 3 ∙ 109 Temperature: 3mK 1 (3s3d) 3D 3 2 (3s3p) 1P1 285 nm 78 MHz 2 1 (3s3p) 3P 0 (3s2) 1S0 Dominika Fim – RTG 1729

7. T-MOT Triplet-MOT: Number of atoms: ̴ 108 Temperature: 1mK Singlet Triplet 1 (3s3d) 3D 3 2 (3s3p) 1P1 383 nm 26 MHz Decay of the number of atoms: α - one-body losses β - two-body losses Ʈ = 1/α̴ 1 s (decay: 3P1→1S0 ) Two-body loss at high number of atoms 285 nm 78 MHz Sequential loading scheme: Atoms in the dipole trap: 3P2 state limited by binary collisions and density 2 1 (3s3p) 3P 0 457 nm 36 Hz (3s2) 1S0 Numberof atoms: T-MOT Trap time tdec / s Dominika Fim – RTG 1729

8. Continuous- loading scheme Triplet Singlet 1 (3s3d) 3D 3 2 383 nm 26 MHz (3s3p) 1P1 285 nm 78 MHz 2 1 (3s3p) 3P 0 457 nm 36 Hz (3s2) 1S0 Dominika Fim – RTG 1729

9. Comparison of the loading schemes loading: dipoletrap Lifetime of the dipole trap 1064 nm Dipole trap 383 nm g = 26 MHz continuousτ=4,5 s Number of atoms N Atomzahl Atomzahl Number of atoms N S-MOT 285 nm g = 79 MHz 457 nm g = 36 Hz sequentialτ=1,1 s T-MOT - 3P0 repumper loading time / s capture 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

10. Enhancement of the loading rate → Density limitation: high photon scattering rate (reabsorption, inelastic collisions) → Optimization only for the continuous loading scheme Higher loadingefficiency due tohigherIntensity • spatial expansion of the T-MOT • (limited by temperature) • → low detuning • → high intensity W0= 3.1 mm W0= 11 mm Numberof atoms in thedipoletrap Saturation on 3P2 → 3D3 Dominika Fim – RTG 1729

11. Decay curve • small number of atoms: exponential decay • high number of atoms: loss attributed to binary collisions RaiseofTemperature → elasticcollisionsratherunlikely → inelastischecollisions Dominika Fim – RTG 1729

12. Inelastic collisions Ʈ = 1/α = 4.2 s A high energy difference requires a low distance → rather unlikely Singulett Triplett 1 (3s3d) 3D 3 2 (3s4s) 1S0 0,024 eV 3P0 + 3P0 3P0 + 3P0 (3s3p) 1P1 (3s2)1S0 + (3s4s)1S0 2 1 (3s3p) 3P 0 (3s2) 1S0 Energie Energie 2,7 eV 2,7 eV Due to the collision both atoms change their atomic state → for the low energy difference collision at high distances possible 1S0 + 3P0 1S0 + 3P0 Dominika Fim – RTG 1729

13. Results Number of atoms: Stepwise: 1.1 ∙ 103 Continuous: 4.5 ∙ 103 Optimized continuous: 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

14. …due to the continuous loading scheme Singulett Triplett 1 (3s3d) 3D 3 ...we were able to trap magnesium atoms in an optical lattice 2 383 nm 26 MHz (3s3p) 1P1 285 nm 78 MHz 2 1 (3s3p) 3P 0 457 nm 36 Hz (3s2) 1S0 10.000 Atome in 3s !! Dominika Fim – RTG 1729

15. Conclusion • Presented a continuous loading scheme for3P0whichavoidsdensitylimitationbyintroducingadditional losschannelto 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 Dominika Fim – RTG 1729 15

16. Group leader… Prof. Dr. Wolfgang Ertmer Prof. Dr. Ernst M. Rasel Dominika Fim – RTG 1729

17. …and the magnesium Team