Photoassociation Spectroscopy of Ultracold MoleculesLiantuan XIAO

State Key Laboratory of Quantum Optics and Quantum Optics Devices,Institute of Laser Spectroscopy, Shanxi University, P.R.China NSFC-ISF Joint Workshop on BEC and Ultracold Phenomena25, Sep. 2013Atom/MoleculePhoton

CollaboratorsPIs:Prof. Liantuan XiaoProf. Suotang JiaExperiment:Dr. Yanting ZhaoDr. Jie MaDr. Jizhou WuDr. Zhonghua JiYichi Zhang (PhD) Yuqing Li (PhD)Jinpeng Yuan (PhD)

Theory: Dr. Gang Chen, Dr. Yongang Yang

OutlineBackground---Ultracold molecules formationExperimental detection technique ---Trap Loss Detection (TLD) ---Ionization Detection (ID)Experimental results---High sensitive spectroscopyConclusion Photoassociation Spectroscopy of Ultracold MoleculesBackground---Ultracold molecules formationExperimental detection technique ---Trap Loss Detection (TLD) ---Ionization Detection (ID)Experimental results---High sensitive spectroscopyConclusion Photoassociation Spectroscopy of Ultracold 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

Why cold molecules?[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.

1) Buffer gas cooling2) Stark cooling 3) V-selected cooling1) Feshbach resonanceHow to form ultracold moleculesDirectIndirect2) Photoassociation

OutlineBackground---Ultracold molecules formationExperimental detection technique ---Trap Loss Detection (TLD) ---Ionization Detection (ID)Experimental results---High sensitive spectroscopyConclusion Photoassociation Spectroscopy of Ultracold MoleculesPhotoassociation Spectroscopy of Ultracold Molecules

Photoassociation (PA) of cold atoms: PA process for a pair of cold Cs atoms. Cs2 and RbCs

* 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.

* 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. 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.

OutlineBackground---Ultracold molecules formationExperimental detection technique ---Trap Loss Detection (TLD) ---Ionization Detection (ID)Experimental results---High sensitive spectroscopyConclusionPhotoassociation Spectroscopy of Ultracold Cesium MoleculesPhotoassociation Spectroscopy of Ultracold Cesium Molecules

(a) Experimental setup. (b) Detection scheme of the three dimensional fluorescence modulation spectroscopy of ultracold molecules.Improve the trap loss spectrum sensitivity---Three-dimensional fluorescence modulation spectroscopy PS: The detail of three-dimensional fluorescence modulation spectroscopy is in the paper ( Phys. Chem. Chem. Phys. 13 (2011) 18921 )

Three dimensions velocity selective spectroscopyProbe laser frequency modulated means to detect partial atoms being selected.Fluorescence intensity modulatedModulated fluorescenceDemodulated spectrumA: modulation amplitudef : modulation frequency

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.J. Mol. Spectrosc., 255, 106 (2009).1Vibrational spectroscopy of excited states of ultracold Cs2Setup

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.Opt. Express, 18, 17090 (2010)2Rovibrational spectroscopy of excited states of ultracold Cs2Dependence of the level intervals on the rotational quantum number JDependence of the rotational constant B on the vibrational number

According to the calculated Franck-Condon factor, as a function of the vibrational level for PA transition of the Cs2 0g- (6P3/2) outer well, the intensity of the trap loss spectra of the lowest level are very small. 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)3PA spectrum of the lowest v excited state of ultracold Cs2---v=2,3Theoretical Franck-Condon factor of Cs2 0g- (6P3/2)PA spectra of the vibrational state (v=3)PA spectra of the lowest vibrational state (v=2)

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

4Determination of laser-induced frequency shifts of ultracold Cs2(a) Laser-induced frequency shift of the PA resonance as a function of PA laser intensity for different rotational progressions (J=2,3,4) of v=17 of the 0g long-range state and (b) different molecular vibrational bound states.Optics Letters , 36, 2038 (2011). 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.

5Direct measurement of laser-induced frequency shift rate of ultracold Cs2We 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. Appl. Phys. Lett. , 101, 131114 (2012)The inset sketch shows the LIFS rate achieved in the same experimental conditions.

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

6Photoassociation spectrum of ultracold RbCs molecules by ionization detectionRbCs photoassociation spectrum in v=10, (4)0-, correlated to (2)3Rotational constant is 0.01304cm-1 and the distortion constant is 0.000015cm-1.

7The electric dipole moment measurement of RbCs moleculesThe measured electric dipole moment the observed RbCs molecules in v=10, (4)0-, correlated to (2)3state is 4.70.6Debye by dc Stark effect.Phys. Rev. A, 85, 013401 (2012)

8The photoassociation lineshape analysis of ultracold RbCs moleculesIntensity and FWHM fitting by wigner formulaSpectroscopy intensity vs ionization laser energyThe intensity vs PA laser intensityThe FWHM vs PA laser intensityTwo-photon photoionization rateJ. Phys. Soc. Jap. 82 084301 (2013)Using the ionization detection, we observe the saturation of PA process and the suppression of ionization process.

OutlineBackground---Ultracold molecules formationExperimental detection technique ---Trap Loss Detection (TLD) ---Ionization Detection (ID)Experimental results---High sensitive spectroscopyConclusionPhotoassociation Spectroscopy of Ultracold MoleculesPhotoassociation Spectroscopy of Ultracold Molecules

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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