observation of bec in the tight binding limit and quantum optics research in siom of cas wang yu-zhu...

Observation of BEC in the Tight Binding Limit and Quantum Optics Research in

SIOM of CAS

Wang Yu-zhu

Key Laboratory for Quantum Optics

Shanghai Institute of Optics and Fine Mechanics

Chinese Academy of SciencesWorkshop on Atomic Bose-Einstein Condensates

Celebrating the Einstein Year of Physics

Beijing, Nov. 23th, 2005

Nembers of our groups:

Liu Liang, (Prof.), He Huijuan, (Prof.)

Hu Zhengfen(Asoc.Prof.), Fu Haixiang (Asoc.Prof.),

Zhou Shuyu, Wei Rong, Den Janliao, Liao Jun, Cheng Huadong,

Xu Zhen, Lv Deshang, Qu Qiuzhi, Li Tian, Xu Xinping, Zhang Wentao,

Li Xiaolin, Ke Ming, Bian Fengang, Zhang Ponfei, Ma Yisheng, Ma Hongyu, zhang Yu.

Den Lu(US), Long Quan(US),Yin Jianping,Hong Tao(US), Lv Baolong, Li Yongqing,Wang Xinqi , Xu Xinye(US).

1.Identify the formation of a Bose-Einstein condensate in tight confinement.

2.Study of Atom Chip with cold atoms.

3.Study of cold atomic clock (Space clock).

4. Superluminal and slow light propagation in gas medium.

Experimental set-up of BEC

Quadrupole Ioffe Configuration(QUIC) Magnetic Trap

Heansch’s group proposed QUIC trap

Identify the formation of a Bose-Einstein condensate :

(1) The sudden increase in the density of the cloud. (2) The sudden appearance of a bimodal cloud

consisting of a diffuse normal component and a dense core (the condensate).

(3) The velocity distribution of the condensate was anisotropic in contrast to the isotropic expansion of the normal (non-condensed) component.

(4) The good agreement between the predicted and measured transition temperatures.

The sudden appearance of a bimodal cloud consisting of a diffuse normal component and a dense core (the condensate).

B=5G B=0.5G

3 July 2002

We have just received the following report of production of a Bose-Einstein condensate in Shanghai:

BEC in 87Rb has been achieved at the Laboratory for Quantum Optics in the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences.

The first evidence of quantum phase transition after rf-evaporation cooling was observed on the 19th of March 2002. After some improvement of our imaging system and magnetic current power, the bimodal distribution of atom cloud can be now seen more clearly and repeatedly.

Our experimental details: we employ a standard double vacuum-chamber system. Cold atoms collected in the upper MOT are continuously loaded into the lower MOT by light pressure force. Within 15 s, about 6 x 108 atoms are trapped in the lower MOT with a temperature 210 microKelvin. Then the transferring light is cut off and a 5-10 ms optical molasses cooling is applied. After that 3 x 10 8 atoms are left with a temperature 20 microKelvin. In about 2 ms atoms are optically pumped onto a weak-field-seeker state, and loaded into a quadrupole magnetic trap with an efficiency of about 30%. Then atoms are compressed by ramping up the magnitude of quadrupole trap, and the atomic temperature increases to 150 microKelvin. Atoms are then adiabatically transferred to a QUIC trap in 1-2s. About 1 x 10 8 atoms are detected in QUIC trap and the lifetime of atoms is about 50s. The radial and axial oscillation frequencies are 150Hz and 14Hz, respectively. The bias magnetic field is 5.4 Gauss. By logarithmically scanning rf frequency from 15 MHz to 3.77 MHz in 19 s and waiting for 100 ms re-thermalization, the absorption image of atom cloud is detected in-situ by a CCD camera. We observe distinct halo appearing around atom cloud near phase transition point, due to the diffraction- limited resolution of imaging system (top frames of figure). To correctly estimate the temperature, we adiabatically ramp down the trap magnitude (with cloud size enlarged and temperature decreased but phase density unchanged) within 1s, pictures are then taken 100 ms after the relaxation (bottom frames of figure.

Everyone engaged in practical work must investigate conditions at the lower levels

Is it possible to observe the BEC directly by Is it possible to observe the BEC directly by absorption imaging ?absorption imaging ?

M. R. Anderson et al, Science, 273, 84(1996).

““We attempted to observe the BEC directly by We attempted to observe the BEC directly by absorption imaging, but failed because of the high absorption imaging, but failed because of the high optical density of the atom cloud near the critical optical density of the atom cloud near the critical temperature” . temperature” .

““The effective area of the atomic cloud is The effective area of the atomic cloud is approximately linearly related to the approximately linearly related to the temperature. “temperature. “

““The sudden decrease in area at the onset The sudden decrease in area at the onset of the evaporative cooling is a sensitive of the evaporative cooling is a sensitive indicator for the phase transitionindicator for the phase transition .” .”

M. R. Anderson et al, Science, 273, 84(1996).

Absorption image of the cloud along X-axis

Absorption image of the cloud along Y-axis

Detection Set-up

Detection

Special resolution: 15μm

Identification of the phase transition by absorption imaging of the probe beam

Sudden decreasing of the temperature of the cloud

20 40 60 80 100 120 140-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

Pixel

物质波的超辐射Experimental results

L.You, Maciej Lewenstein,Near-Resonant Imaging of Trapped Cold Atomic Samples,Journal of Research of the National Institute of Stands and Technology,Volume 101,Number 4 July-August 1996;

R.J.Glauber, in Lectures in Theoretical Physics, W.E.Brittin and L.G.Dunham, eds,.Vol.I,Interscience,New York(1959)p.315

Theoretical results

Comparesion of theoretical and experimental Results

L.You, Maciej Lewenstein,Near-Resonant Imaging of Trapped Cold Atomic Samples,Journal of Research of the National Institute of Stands and Technology,Volume 101,Number 4 July-August 1996;

R.J.Glauber, in Lectures in Theoretical Physics, W.E.Brittin and L.G.Dunham, eds,.Vol.I,Interscience,New York(1959)p.315

New QUIC magnetic trap

I =25A o , s 200

T=320nk

T<150nK Tc=220nK

t=6ms t =10ms t=17 ms t=18 ms

Atom Chip

1.H-atom chip study

2.RF atom chip

The first Chinese atom chip

I

I

II

Bias-Coil

MOT Coil

detection

Trapping beam

Si Base

(Gold thin film ）

Periodic magnetic microtraps experiment process

Periodic magnetic microtraps experiment process

MOT to trap cold atoms for the chip

Experimental set-up of the atom chip

Cold atom number

N=

in the MOT

1x106

1x105

Cold atom number

N=

in the MOT on the chip

Atom Chip-a RF magnetic trap of cold atoms

Magnetic trap can confine atoms in weak-field seeking states, the atoms are susceptible to two-body hyperfine or Zeeman level exchanging collisions.

We proposed an ac magnetic field trap, which is based on the interaction of magnetic dipole moment of atom with both ac quadurpole magnetic field and a dc magnetic field.

Lifang Xu, Jianping Yin and Yuzhu Wang, Optics Commun., 188,93(2001) "A proposal for ac magnetic guide and trap of cold atoms "

2/121

201 ))/(( BBBe

RF-magnetic trap

222

220

2222

00

])()[(

)(4

B

BBBgUF B

X

Y

B0

RF Signal

RF Signal

R.F. ω=26.4MHz

R. Current I=1.5A

Bias field B0=2.1Gauss

Deep of the trap 200μK

RF-Atomchip Program Collaborator:

Prof Jiuyao Tang Department of Physics, Zhejiang University

Prof Weijia Wen Department of Physics, Hongkong University of Science and Technology

Picture of the RF-atom chip

Interference of mater wave

Beam splitter

原子喷泉研究 ( Atomic fountain clock)

Purpose of the research:

To build a movable atomic clock .

To develop technique of space atomic clock.

Paris Observatory

Probe type of an atomic fountain clock

Probe type of the movable atomic fountain clock.

Vacuum in the chamber: p~5x10(-10)Torr.

Micro-wave cavity

Measurement of the Q factor

在微波中心频率的右边，微波功率下降 2.95dB 时，频率偏差为 190kHz 。

这样可以看出微波腔的带宽大约为 380kHz 。微波腔的有载 Q 值为 17986 。

选态腔 : 微波功率下降 3.00dB 时，频率偏差为 840kHz 。微波腔的有载 Q 值为 4298.5 。

Measurem-ent of the residual magnetic field in thevacuum chamber.

∆B < 10nG

0.2 0.3 0.4 0.5 0.6 0.7 0.8-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

Va

lue

(v

)

T im e Delay (s)

High of lunching 50-80cm

0.0 0.4 0.8 1.2 1.6 2.0107

108

Tossing Detuning (MHz)

Ato

mic

Num

ber

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

2

3

4

5

6

7

8

9

10

Tossing Detuning (MHz)

Tem

per

atu

re

()

Superluminal propagation

Hanle 组态 (Hanle configuration)

5P1/ 2 -2 -1 0 1 2 m f

5P1/ 2 -2 -1 0 1 2

-1 0 1

5S ½ -2 -1 0 1 2 m f

)11(2/1

)11(2/1

22

12

mmD

mmD

Double dark state ：

EITand EIA Superluminal light ：

F=2

F’=1

F’=2

arXiv:quant-ph/0309171 v1

Texas A&M University

12 ' FF 22 ' FF

middle

F=2 F’=1

F=2 F’=2

No buffer gas

0BgmE F 0 l

Dispersion like line shape

The Kramers-Kronig relations enable us to find the real part of the response of a linear passive system if we know the imaginary part of the response at all frequencies, and vice versus.


= -1s

10s

-2s


Signal speed vi , start point of the pulse vi = c 。

= -1s

Start point, vi = CStart point, vi = C

X 4

10s -2s

Start point ,vi = C

Start point ,vi = C

X 4

Signal speed vi , start point of the pulse vi = c 。

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Key Laboratory for Quantum Optics

Shanghai Institute of Optics and Fine Mechnics