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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.
Superluminal propagation
= -1s
10s
-2s
Superluminal propagation
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 。
Welcome to Join Us!
Thanks!
Key Laboratory for Quantum Optics
Shanghai Institute of Optics and Fine Mechnics