Photoassociation Spectroscopy of Ultracold Molecules

1. NSFC-ISF Joint Workshop on BEC and Ultracold Phenomena Photoassociation Spectroscopy of Ultracold Molecules Liantuan XIAO State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, P.R.China Photon Atom/Molecule 25, Sep. 2013

2. Collaborators Experiment: Dr. Yanting Zhao Dr. Jie Ma Dr. Jizhou Wu Dr. Zhonghua Ji Yichi Zhang (PhD) Yuqing Li (PhD) Jinpeng Yuan (PhD) PIs: Prof. Liantuan Xiao Prof. Suotang Jia Theory: Dr. Gang Chen, Dr. Yongang Yang

3. Photoassociation Spectroscopy of Ultracold Molecules Outline • Background---Ultracold molecules formation • Experimental detection technique • ---Trap Loss Detection (TLD) • ---Ionization Detection (ID) • Experimental results---High sensitive spectroscopy • Conclusion • Background---Ultracold molecules formation • Experimental detection technique • ---Trap Loss Detection (TLD) • ---Ionization Detection (ID) • Experimental results---High sensitive spectroscopy • Conclusion Photoassociation Spectroscopy of Ultracold Molecules

4. Why cold molecules? • 1. Fundamental research • * High resolution molecular spectroscopy • * Weak interaction in molecules • 2. Superchemistry • * Elastic and inelastic cold collisions • * Cold chemistry. • 3. Solid state physics generated by an ultracold dilute ensemble • * Observation of BEC with molecules • * Investigation of dipole-dipole interactions of polar • molecules. • 4. Quantum computation [1] John M. Doyle, Bretisiav Friedrich. Nature. (1999) Vol. 401, 749. [2] K. M. Jones, E. Tiesinga, P. D. Lett, P. S. Julienne. Rev. Mod. Phys. (2006) Vol. 78, 483.

5. How to form ultracold molecules： Indirect Direct 1) Buffer gas cooling 1) Feshbachresonance 2) Stark cooling 2) Photoassociation 3) V-​​selected cooling

6. Photoassociation Spectroscopy of Ultracold Molecules Outline • Background---Ultracold molecules formation • Experimental detection technique • ---Trap Loss Detection (TLD) • ---Ionization Detection (ID) • Experimental results---High sensitive spectroscopy • Conclusion Photoassociation Spectroscopy of Ultracold Molecules

7. Photoassociation (1) Resonant photon absorption by two cold atoms (T~10uK) (1) (2) Deexcitation (2’) free Atoms Cold molecules (2) (2') Photoassociation (PA)of cold atoms: Cs2 and RbCs PA process for a pair of cold Cs atoms.

8. Cold Molecules detection: * PA spectroscopy of ultracold atoms provides information on the molecular excited state levels which is essential for determination of the molecular parameters, and therefore for potential curves. * The ion spectrum, shows the ions yield obtained by photoionisation of the stable ultracold molecules created either in the ground state or in the lowest triplet state. The electronically excited molecules formed by PA have a too short lifetime to give a significant contribution to the photoionisation signal. • * The trap-loss spectrum, reveals virotational progressions for all attractive potentials which can be reached by PA. • The decay into either a pair of hot atoms, or a stable molecule, induces a decrease of the atom trap fluorescence.

9. Photoassociation Spectroscopy of Ultracold Cesium Molecules Outline • Background---Ultracold molecules formation • Experimental detection technique • ---Trap Loss Detection (TLD) • ---Ionization Detection (ID) • Experimental results---High sensitive spectroscopy • Conclusion Photoassociation Spectroscopy of Ultracold Cesium Molecules

10. We have compared the spectral signal by using direct trap loss detection with three dimensional fluorescence modulation spectroscopy. Under the same conditions, signal to noise ratio (SNR) of three dimensional modulation spectroscopy had increased by more than 20 times than the direct trap loss spectroscopy ! Improve the trap loss spectrum sensitivity ---Three-dimensional fluorescence modulation spectroscopy (a) Experimental setup. (b)Detection scheme of the three dimensional fluorescence modulation spectroscopy of ultracold molecules. PS: The detail of three-dimensional fluorescence modulation spectroscopy is in the paper ( Phys. Chem. Chem. Phys. 13 (2011) 18921 )

11. Three dimensions velocity selective spectroscopy Fluorescence emit rate： Δl：probe laser detune A: modulation amplitude f : modulation frequency Fluorescence intensity modulated Probe laser frequency modulated means to detect partial atoms being selected. Modulated fluorescence Demodulated spectrum

12. 1、Vibrational spectroscopy of excited states of ultracold Cs2 Setup J. Mol. Spectrosc., 255, 106(2009). By using the three-dimensional modulation spectroscopy the signal-to-noise ratio of the spectra is improved and ultimately the PA spectra obtained by detecting trap loss are extended to a red detuning of ~70 cm-1 below the dissociation limit.

13. 2、Rovibrational spectroscopy of excited states of ultracold Cs2 Dependence of the level intervals on the rotational quantum number J The low-lying vibrational spectroscopy of Cs2 0g- pure long-range state have been observed with rotational structures, which are well resolved up to J=0~8. The rotational constants are obtained by fitting experimental data to a nonrigid rotation model. Dependence of the rotational constant B on the vibrational numberυ Opt. Express, 18, 17090 (2010)

14. 3、PA spectrum of the lowest v excited state of ultracold Cs2---v=2,3 According to the calculated Franck-Condon factor, as afunction of the vibrational level for PA transition of the Cs2 0g- (6P3/2) outer well,the intensity of the trap lossspectra of the lowest level are very small. PA spectra of the vibrational state (v=3) Theoretical Franck-Condon factor of Cs2 0g- (6P3/2) The v = 2 and 3 vibrational levels of the pure long-range state 0g- (6P3/2) of cesium molecule are detected directly with high rotational resolution. Phys. Chem. Chem. Phys., 13, 18921 (2011) PA spectra of the lowest vibrational state (v=2)

15. 3、PA spectrum of the lowest v excited state of ultracold Cs2---v=0,1

16. 4、Determination of laser-induced frequency shifts of ultracold Cs2 We experimentally present a technique for sensitively determining the laser-induced frequency shifts of the ultracold cesium molecular vibrational and rotational levels. The scheme relies on an optical frequency shifter, leading to two laser beams with a precise and adjustable frequency interval. (a) Laser-induced frequency shift of thePA resonance as a function of PA laser intensity for differentrotational progressions (J=2,3,4)of v=17 of the 0g−long-range state and (b) different molecular vibrational boundstates. Optics Letters , 36, 2038 (2011).

17. 5、Direct measurement of laser-induced frequency shift rate of ultracold Cs2 We carried on a quantitative determination of the laser-induced frequency shift rate of the ultracold Cs2 formed via PA by means of the trap loss measurement of the losses of trapped atoms in a standard magneto-optical trap. The experiment was directly performed by varying the photoassociation laser intensity without any additional frequency monitor technologies. The inset sketch shows the LIFS rate achieved in the same experimental conditions. Appl. Phys. Lett. , 101, 131114 (2012)

18. Comparison between homonuclear and heteronuclear molecules RbCs molecular potential energy curves and ionization detection process PA probability is lower for heteronuclear molecules. The ionization detection is a good method for heteronuclear molecules

19. RbCs+ molecular ion with and without PA laser 6、Photoassociation spectrum of ultracold RbCs molecules by ionization detection RbCs photoassociation spectrum in v=10, (4)0-, correlated to (2)3Π Rotational constant is 0.01304cm-1 and the distortion constant is 0.000015cm-1.

20. J=0， J≠0 7、The electric dipole moment measurement of RbCs molecules The measured electricdipole moment the observed RbCs molecules in v=10, (4)0-, correlated to (2)3Πstate is 4.7±0.6Debye by dc Stark effect. Phys. Rev. A, 85, 013401 (2012)

21. 8、The photoassociation lineshape analysis of ultracold RbCs molecules Intensity and FWHM fitting by wigner formula Spectroscopy intensity vs ionization laser energy Two-photon photoionization rate： The intensity vs PA laser intensity The FWHM vs PA laser intensity Using the ionization detection, we observe the saturation of PA process and the suppression of ionization process. J. Phys. Soc. Jap. 82 084301 (2013)

22. Photoassociation Spectroscopy of Ultracold Molecules Outline • Background---Ultracold molecules formation • Experimental detection technique • ---Trap Loss Detection (TLD) • ---Ionization Detection (ID) • Experimental results---High sensitive spectroscopy • Conclusion Photoassociation Spectroscopy of Ultracold Molecules

23. Conclusion • Two detection technology in photoassociative molecules ◆ Improved Trap loss detection in homonuclear molecules ◆Ionization detection in heteronuclear molecules • Based on the high sensitive detection methods • ◆PA spectroscopy of excited states of ultracold Cs2 and RbCs • ◆ Precision measurement of LIFS rate for Cs2 • ◆ The electric dipole moment measurement of RbCs • ◆ The photoassociation lineshape analysis of ultracold RbCs

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