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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.

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photoassociation spectroscopy of ultracold molecules

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

slide2

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

slide3

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

slide4

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.

slide5

How to form ultracold molecules:

Indirect

Direct

1) Buffer gas cooling

1) Feshbachresonance

2) Stark cooling

2) Photoassociation

3) V-​​selected cooling

slide6

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

slide7

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.

slide8

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.
slide9

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

slide10

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 )

slide11

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

slide12

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.

slide13

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)

slide14

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)

slide16

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).

slide17

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)

slide18

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

slide19

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.

slide20

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)

slide21

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)

slide22

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

slide23

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
slide24

Thanks for your attention!

Welcome to Institute of Laser Spectroscopy@Shanxi University

http://laserspec.sxu.edu.cn/

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