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 NSFC-ISF Joint Workshop on BEC and Ultracold Phenomena 25, Sep Atom/Molecule Photon

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

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 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

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 cooling 2) Stark cooling 3) V- ​​ selected cooling 1) Feshbach resonance How to form ultracold molecules ： Direct Indirect 2) Photoassociation

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

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

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

(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 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 ! PS: The detail of three-dimensional fluorescence modulation spectroscopy is in the paper ( Phys. Chem. Chem. Phys. 13 (2011) )

Three dimensions velocity selective spectroscopy Fluorescence emit rate ： Δ l ： probe laser detune Probe laser frequency modulated means to detect partial atoms being selected. Fluorescence intensity modulated Modulated fluorescence Demodulated spectrum A: modulation amplitude f : 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). 1 、 Vibrational spectroscopy of excited states of ultracold Cs 2 Setup

The low-lying vibrational spectroscopy of Cs 2 0 g - 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, (2010) 2 、 Rovibrational spectroscopy of excited states of ultracold Cs 2 Dependence of the level intervals on the rotational quantum number J Dependence of the rotational constant B on the vibrational numberυ

According to the calculated Franck-Condon factor, as a function of the vibrational level for PA transition of the Cs 2 0 g - (6P 3/2 ) 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, (2011) 3 、 PA spectrum of the lowest v excited state of ultracold Cs 2 ---v=2,3 Theoretical Franck-Condon factor of Cs 2 0 g - (6P 3/2 ) PA spectra of the vibrational state (v=3) PA spectra of the lowest vibrational state (v=2)

3 、 PA spectrum of the lowest v excited state of ultracold Cs 2 ---v=0,1

4 、 Determination of laser-induced frequency shifts of ultracold Cs 2 (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 0 g − 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.

5 、 Direct measurement of laser-induced frequency shift rate of ultracold Cs 2 We carried on a quantitative determination of the laser- induced frequency shift rate of the ultracold Cs 2 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, (2012) The inset sketch shows the LIFS rate achieved in the same experimental conditions.

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

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

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

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

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

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 Cs 2 and RbCs ◆ Precision measurement of LIFS rate for Cs 2 ◆ The electric dipole moment measurement of RbCs ◆ The photoassociation lineshape analysis of ultracold RbCs

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