三维光晶格和原位测量-物
理所 BEC研究展望
王如泉
中国科学院物理研究所
第五届全国冷原子物理和量子信息青年
学者学术讨论会
兰州大学 2010. 8. 4
Outline
1. Why is in situ imaging important
2. The BEC setup at IOP and our in situ
imaging plan
3. The
87Rb-40K-23Na(6Li)
project at IOP
BEC – coherent macroscopic matter wave
Vortex in BEC
(JILA group, 2000)
BEC of
87Rb
(JILA group, 1995)
Ideal platform for Ultra low
temperature quantum physics
Matter wave laser
(MPQ group, 2000)
lamp
laser
Matter wave
interference
(MIT group, 1997)
Quantum simulation of many body physics
什么是量子仿真?
强关联多体物理：
是物理学尚未攻克的难关，又是决定诸
多材料物性的关键（铁磁性，巨磁电阻，
重费米子，高温超导等）
原因:
1.多体波函数,全量子系统
新材料探索:
超导, 磁性等
量子计算机:
光晶格中的原子气
2.非线性系统，无法用微扰论处理
数值仿真
计算资源随系统粒子数指数增长
解决方案之一：
基本模型研究:
Hubbard模型,
Heisenberg模型等
用量子计算机仿真量子系统
Qi Zhou et al, PRL 103, 085701 (2009)
特殊的量子计算机-量子仿真器
Quantum simulation of many body physics
Qi Zhou et al, PRL 103, 085701 (2009)
First quantum simulation experiment
looks beautiful, but faces a lot of questions
Super fluid to Mott insulator phase
transition in 3-D optical lattice
3D optical lattice
•
•
•
•
•
Quantum degenerate Bose/Fermi system
below micro Kelvin
Optical lattice provide periodical potential
with no defects
Atom-atom interaction can be described by a
simple s-wave scattering length
Easily tunable Hubbard Model parameters
Artificial toy models: 1D, 2D, spinor, etc
Greiner M., Mandel O., Esslinger T., Hansch T.
W. & Bloch I., Nature 415, 39–44 (2002).
• Lack of a clear diagnostic of how
to identify phases
• Complications due to
coexistence of different phases
in the same confining potential
• Lack of thermometry of the Bose
gas in the optical lattice
Time of flight (TOF) imaging
TOF imaging of BEC @ IOP
BEC的相变过程
0ms
10ms
20ms
各向异性膨胀
30ms
Problem with TOF measurement
Qi Zhou et al, PRL 103, 085701 (2009)
In-situ imaging: corner
stone setting experiment by
Chin’s group at Chicago
Absorption imaging of density profile
of thin layer cold atoms in 2-D optical
lattice with a high numerical aperture
imaging lens.
Gemelke, N., Zhang, X., Hung, C.-L. & Chin, Nature, 460, 995 (2009)
I. Bloch’s group’s work to resolve single lattice site
I. Bloch et al, Nature, 467, 68(2010)
Melting of a Mott insulator
M. Greiner’s group to achieve single lattice resolution
W. S. Bakr, J. I. Gillen, M. Greiner et al, Nature, 462, 74(2009)
Wedding cake structure of the Mott insulator
W. S. Bakr, M. Greiner et al, Science, 329, 547(2010)
What can we achieve with in situ imaging of number density
Determine the superfluid density, temperature
and chemical potential of the trapped system
with high accuracy, critical for mapping out the
phase diagram at finite temperature
Qi Zhou et al, PRL 103, 085701 (2009)
Tin-Lun Ho and Qi Zhou，NATURE PHYSICS 6, 131(2009）
Single Chamber BEC @ IOP
Single chamber design vs Double MOT design:
advantages and disadvantages
Single chamber
Double MOT
Vacuum system
1 chamber and 1 set of
pumping system
2 chambers and 2 sets
of pumping system
Laser cooling
system
6 laser beams
13 laser beams
Optical access
4 free directions
2D optical lattice
3 free directions
1D optical lattice
No of atoms
1x105
(2-5)x105
Light-Induced Atomic Desorption for loading a Rubidium
Magneto-Optical Trap
MOT loading at different LED current
500mA
411mA
310mA
200mA
100mA
25mA
0mA
9
2.0x10
9
atom
1.5x10
9
1.0x10
8
5.0x10
0.0
0
10
20
30
40
time (s)
50
60
70
80
Vacuum restoring time
8
4.0x10
rate decay
LED current 500mA
8
2.0x10
0.0
0
100
200
time (s)
Fast decay 2s
Slow decay 50s
300
Quadruple trap
B  0
dBx dBy
dBz


dx
dy
dz
B0
Phys. Rev. A, 35, 1535(1987)
Magnetic atom transfer belt
冷原子团
转移线圈
Phys. Rev. A, 63, 031401(2001)
Transfer coils geometry
线圈
重
力
方
向
MOT
内半径 外半径
线直径
厚度mm
填充率
mm
mm
mm
15.0
1.6
62%
30.0
50.0
TC
10.0
40.0
15.0
1.6
62%
QUIC
15.0
50.0
10.0
1.6
62%
保持转移方向的磁场
梯度为75G/cm
Field Plot during the transferring process
Transfer coil 3D lattice and Ultra high resolution in situ imaging
MOT
BEC
lattice
Imaging lens
CCD camera
CCD camera
Large numerical aperture long working distance objectives
Group
Objective
M. Greiner
18mm 0.55(to 0.8)
I. Bloch
13mm 0.68(Leica)
C. Chin
Resolution 3-4um
D. S. Weiss
16mm 0.55
M. Karski
0.29
Company
Product specification
Work distance/mm
NA
Zeiss
Epiplan-Neofluar
50x/0.55 HD DIC M27
9.0
0.55
Olympus
SLMPLN100x
7.6
0.6
Leica
HCX PL FLUOTAR L
40x/0.60 CORR
3.3
0.6
Nikon
ELWD 50x
8.7
0.55
Mitutoyo
M Plan Apo 100x
G Plan Apo 50x
6
15.08
0.7
0.5
EMCCD camera
Spatial resolved single photon detection
Group
CCD
M. Greiner
EMCCD (Andor Ixon DU888)
I. Bloch
EMCCD
C. Chin
Not mentioned
D. S. Weiss
EMCCD
M. Karski
EMCCD
Princeton Instrument ProEM: 512B_eXcelon
Quantum degenerate polar molecules
玻色-费米混合系统（玻色子，费米子到极性分子）
异核偶极分子具有各向异性且长程的偶极-偶极
相互作用，是对关联系统研究具有重要意义。
量子简并
相干态转化
简并玻色-费米混合系统是
得到超冷分子的最优手段
偶极晶体相变，多体
偶极量子气，量子信
息，超冷化学
超冷分子的重要科学意义
New. J. Phys., 11, 055049(2009)
Great achievements and current difficulties
激发态冷分子制备
基态冷分子制备
超冷化学中的量子统计特性
简并偶极分子实验的关键障碍
1. 铷-钾分子偶极矩太小
2. 铷-钾分子在超冷碰撞中不稳定
偶极分子的各向异性
Nature, 424, 47(2003), Science, 301, 1510 (2003), Phys. Rev. Lett. 100, 143201 (2008).
Nature Physics 4, 622 (2008), Phys. Rev. Lett. 100, 143201 (2008), Science, 322, 231
(2008), Science, 327, 853 (2010), Nature, 464, 1324(2010)
The
87Rb-40K-23Na(6Li)
project at IOP
新的原子选择的必要性和优势：40K-23Na
87Rb-40K-23Na（或6Li）混合冷却系统
偶极矩
(Debeye)
稳定性
ΔE(cm-1)
Li-Na
0.56
Li-K
相对碰撞截面
Rb-Rb
1
-328
K-Rb
2
3.6
-534
Li-K
0.2
Li-Rb
4.2
-618
Li-Li
0.1
Li-Cs
5.5
-415
Na-Na
0.72
Na-K
2.8
74.3
Na-K
？
K-Rb
0.6
-8.7
K-Cs
1.9
37.8
J. Chem. Phys. 122,204302 (2005)
40K-23Na具有更大的偶极矩和超冷化学反
应的稳定性，是所有可能中的最佳组合
31
Vacuum system
23Na和7Li同一塞
曼减速器和同一
套染料激光
转移线圈以实
现三维光晶格
和原位测量
磁阱
原位测量空间
分辨优于2微米
32
Laser cooling system
铷原子冷却
激光系统
钾原子冷却
激光系统
钠原子冷却
激光系统
33
Cooling laser for Rb and K
25oC下自由运转波长783nm的激光管冷却到-50oC得到767nm，0.2nm/oC。
困难：冷却到-50C热负载很大且有结露问题，
解决方法：真空隔热和三级制冷。
Cooling laser for Lithium
cooling laser for Li
Optic Spectrometer
not injection locking
7mw injection 45°C
FP cavity signal
8mw injection 45°C
Complete injection locking
partial injection locking
multimode
Complete injection locking
singlemode 224mw output
589nm dye laser for Na cooling
半导体激光的波长覆盖
Na冷却所需的589nm激光不能用半导体激光器
成熟的解决方案是染料激光
同时适用于Na(589nm)和Li (671nm)的冷却
Zeeman slower
塞曼减速器：
适合于原子量较
小的原子，更好
的差分真空泵浦
减速器效能
23Na和7Li的俘获速度不同
塞曼减速器轴向磁场优化结果
但效能和俘获速度无关
23Na和7Li共用塞曼减速器
Atomic transferring belt
• 把原子从磁光阱转移到蒸
发磁阱
• 为三维光晶格和原位测量
等提供可能
研制重点：
复杂的大电流线圈控制电路
Thermal distribution simulation is very important
for high performance magnetic trap
Feshbach coils
强磁场1000G
磁场稳定性<50mG(50ppm)
磁场快速扫描G/us
快速开启(ms)
研制重点：
强磁场的获得
超高的磁场稳定性要求
B0=1007.34G, ΔB=170mG
Phys. Rev. Lett. 89, 283202 (2002)
Optical lattice
2D
3D
激光器：IPG单频光纤激光器
光功率：50W
束腰: 100 µm
研制重点：
Nature, 453, 736 (2008)
Nature physics,1,23(2005)
激光的稳定性
超高光路稳定性
43
Thank you for your attention!