Laboratoire Charles Fabry de l'Institut d'Optique Théorique et Appliquée UMR 8501 du CNRS

1. Single atom manipulationsBenoît Darquié, Silvia Bergamini, Junxiang Zhang, Antoine Browaeys and Philippe Grangier Laboratoire Charles Fabry de l'Institut d'Optique Théorique et Appliquée UMR 8501 du CNRS 91 403 Orsay http://www.iota.u-psud.fr/~grangier/Quantum_optics.html

2. Experience : Context : Goals : two neutral atoms trapped in two different dipole traps confinement :  mm3 a few microns away from one another Introduction study and manipulation of an optical dipole trap for single atoms • entangle the atoms • make a quantum gate

3. |e hw0 hwL laser-induced non-dissipative force associated with a potential energy |g hD atom in the laser field For large detunings d : with : - the Rabi frequency - D the lightshift Principle of a dipole trap Assumption : two-level atom, in a laser-field of frequency wL,with a red detuning : d = wL - w0 < 0. two-level atom Atoms are trapped in the high intensity regions The transition frequency is shifted to the blue

4. We use a magneto-optical trap as a reservoir of cooled atoms : - to trap and cool atoms - to induce the fluorescence of the atoms (which will allow us to observe them) Focussing of a Titanium-Sapphire laser beam in the centre of this reservoir Atoms are gathering at the focussing spot => dipole trap Dimensions of the trap = dimensions of the focussing spot dipole trap Dipole trap Dipole force= non-dissipative force=> we previously have to cool atoms

5. Trapping beam Position of the MOT ~5 cm waist of the beam < 1 mm The microscope objective : MIGOU • Characteristics of MIGOU : • large numerical aperture : 0,7 • diffraction limited spot • large working distance (~1cm) • ultra high vacuum compatible • Double use of MIGOU : • to secure the focussing of the trapping beam in the center of the MOT • to collect the fluorescence of trapped atoms with a large efficiency

6. MOT & dipole trap Vacuum chamber Computers Avalanche Photodiode CCD camera y x z 780 nm filters Spatial filtering Filtering pinhole Dipole trap beam Fluorescence Experimental set-up

7. Y X Pictures of the dipole trap on the CCD camera • Continuous observation of the fluorescence of the • dipole trap on the CCD caméra. • One picture every 200 ms. Fluorescence Fluorescence (CCD) 10 000 counts (200 ms) Y scaling of imaging system : 1 pixel = 1 mm X

8. Images on the CCD camera 5 mm Counting rate (counts/10ms) 120 1 atom 80 40 Background 0 0 5 10 15 20 25 Time (s) Single atom regime

9. MOT & dipole trap What we observe on the CCD caméra 4 mm second trapping beam. Double trap In single atomregime, there are four likely configurations :

10. Temperature of the atoms and trap frequencies • Goals : • Requirements : • entangle the atoms • make a quantum gate • atom in the Lambe-Dicke regime : h << 1 we have to measure the temperature of the atoms and the trap frequencies

11. P(Dt) Dt Oscillation frequencies : principle of the measurement • We trap one atom. • We switch off and on the dipole trap during Dt1. •  If the atom is recaptured, it starts to oscillate in the trap. • We wait for Dt and then, we switch off and on the dipole trap during Dt2. •  P(Dt) is the probability to recapture the atom after the whole sequence. Dipole trap Dt1 Dt2 ON Dt OFF  oscillate at 2fosc.

12. } • w0 = 0.89 mm • Ptrap = 2 mW fr = 140 kHz , fz = 29 kHz Oscillation frequencies : experimental results Ptrap = 1,9 mW Ptrap = 1,5 mW Delay (ms) Dt1 = 1 ms Dt1 = 2.5 ms

13. MOT 1 : We trap one atom Objective Trapping beam Temperature of the atom : time of flight experiments • Time sequence:

14. Objective Trapping beam Temperature of the atom : time of flight experiments • Time sequence: 1 :We trap one atom 2 :We switch off the MOT

15. MOT Objective Trapping beam 4 :We check if the atom is still there Temperature of the atom : time of flight experiments • Time sequence: 1 :We trap one atom 2 :We switch off the MOT 3 :The trapping beam is switched off during Dt  We measure the probability of recapturing the atom after Dt.

16. + P = 2 mW simulation with T = 140 mK simulation with T = 35 mK Temperature of the atom : results T = 35 mK

17. Conclusion and outlooks • We are now able to evaluate the trap frequencies and the temperature of the atoms • We need : • a better confinement • a smaller temperature • Better confinement retro-reflexion of the trapping beam, standing wave • Smaller temperatures  Raman cooling Lamb-Dicke parameters : r  0.5 z  2.5

18. Single atom manipulationsBenoît Darquié, Silvia Bergamini, Junxiang Zhang, Antoine Browaeys and Philippe Grangier Laboratoire Charles Fabry de l'Institut d'Optique Théorique et Appliquée UMR 8501 du CNRS 91 403 Orsay http://www.iota.u-psud.fr/~grangier/Quantum_optics.html

19. |2> |2> probe beam probe beam p p s s |1> |1> |0> |0> Entanglement of two atoms Atome 1 Atome 2 beam splitter detector of p-polarized light:

20. |2> probe beam p s |1> |0> Entanglement of two atoms Excitation by a photon of the probe beam: detection of s-polarized ligt: detection of p-polarized light: atoms behave as Young's slits  interferences projection onto the state:  entanglement

21. Plan of my talk • Principle of the optical dipole trap • Implementing a dipole trapA microscope objective : MIGOUExperimental set-upPictures of the dipole trapDouble dipole trap • Temperature of the atoms • Oscillation frequencies of the dipole trap • Conclusion and outlooks