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8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Spinor BEC andMulti-component Quantum Gases
Jason HoThe Ohio State University
Center for Advanced StudyTsinghua University
December 13, 2005
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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What have we learned ?
What novel things awaiting for us?
What can we do with multi-component
Bose gases?
What is new?
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Spin´ 1/2 : Two different spin states of Rb
Spin-1 : |F=1 > hyperfine state of Rb-87 and Na-23
How do the ground states of these differ from scalar Bose gas and
from each other?
Spin-2 : |F=2 > hyperfine state of Rb-87
Examples of multi-component Bose gas
Do we expect any other ground states beside Bose condensed states?
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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What else besides Bose condensed states?
What are the reasons for un-condensed
ground states in Bose systems?
Why do they occur in multi-component systems?
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Conventional Bose condensate :
all Bosons condenses into a single state.
Vanishing inthermodynamic
limit
3D 1D
No condensation
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What happens when there are several degenerate
state for the Bosons to condensed in?
G: Number of degenerate states N: Number of Bosons
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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What happens when there are several degenerate
state for the Bosons to condense in?
G: Number of degenerate states N: Number of Bosons
Pseudo-spin 1/2 Bose gas: G =2
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Spin-1 Bose gas : G=3, G<<N
G: Number of degenerate states N: Number of Bosons
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Spin-1 Bose gas : G=3, G<<N
Bose gas in optical lattice: G ~N
G: Number of degenerate states N: Number of Bosons
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Spin-1 Bose gas : G=3, G<<N
Bose gas in optical lattice: G ~N
Fast Rotating Bose gas: G>>N
G: Number of degenerate states N: Number of Bosons
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PE : Eigenvalues
RE (&
r ) : EigenfunctionsPE
E0 1 2 3
P0
~ N
P1
,P2
,...~O(1)
Existence of a single macroscopic eigenvalue in
](&r )](
&r ' ) "
](&r )](&r ' ) "! PERE
* (&r )RE (&r ')
E§
Penrose-Onsager characterization of Bose condensation
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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PE
E0 1 2 3
P0
~ N
P1
,P2
,...~O(1)
]
(&r )](
&r ' ) "! ]
(&r ) " ](
&r ' ) "
+ «
Off-Diagonal Oder Phase Coherence
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Other possibilities ?
PE
E
0
1
2
3
P0
~ N
P1
,P2
,...~O(1)
PE
E0 1 2 3
P0
,P1,P
2,...~O(1)
Fragmented condensate
Strongly correlated
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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PE
E
0
1
2
3
P0~ N
PE
E
0
1
2
3
PE
E0 1 2 3
By varying the external environment,
one can go from one regime to another
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Single condensate state of spin-F Bosons
]Q
(&r )]R (
&r ') "! PE f Q
*(E ) (&r ) f R
(E ) (&r ' )
E§
Single particle density matrix contains a single eigenvalue of order N
scalar Spin-1/2 Spin-1
]Q (&
r ) "! =1
=2
¨ª©
¸ º¹
]Q (&r ) "! =
1
=2
=3
¨
ª
©©©
¸
º
¹¹¹
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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H ! ´ !2
2 M ] ] V (
&r )]]
g
2](r )](r )](r )] (r )
«
-¬»
½¼
H ! ´ !2
2 M ]Q
]Q V (r )]Q]Q
1
2 g QR]Q
]R]R]Q
«
-¬»
½¼
Q !o,q
H s
!!
2
2 M ]
Q]
QV (
&r )]
Q]
Q K
& B ]
Q & F QR
]R
«
-
¬
¬
»
½
¼
¼
1
2c
0]Q]
E]
E]Q c
2]Q]
E & F QR
& F EF
]F]R
«-¬
»½¼´́
L]Q ( Ö B
& F )
2«-¬
»½¼
QR
]R
´+
Single component
Two component
Spin-1
T.L. Ho, PR L (98), K . Machida et.al J. Phil Mag (98)
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Internal conversion in Spin-1 and Spin-2 Bose gas
Absent in spin 1/2 Bose gas!
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Can there be other possibilities ?
PE
E
0
1
2
3
P0
~ N
P1
,P2
,...~O(1)
PE
E0 1 2 3
P0
,P1,P
2,...~O(1)
Fragmented condensate
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Bosons in double well:
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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t
1 2Bose gas in double well <==> A simple model of
two component Bose gas
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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A Quick Overview
What we have now and what we look for.
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Condensed
Fast Rotating : Great varietyof vortex lattices
Optical lattice: new states
Coherent Spin dynamics
From highly correlated toGeneralized Schrodinger cats
New quantum Hall states
Very rich correlated structures
Quantum Spin dynamics
Uncondensated
Textures New type of excitations
Low dimension: New solitons
New 1D and 2D correlated states
Spin 1/2
Spin-1
Spin-2
Coreless vortex
Spinor BEC
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Condensed
Fast Rotating : Great varietyof vortex lattices
Optical lattice: new states
Coherent Spin dynamics
From highly correlated toGeneralized Schrodinger cats
New quantum Hall states
Very rich correlated structures
Quantum Spin dynamics
Uncondensated
Textures New type of excitations
Low dimension: New solitons
New 1D and 2D correlated states
Spin 1/2
Spin-1
Spin-2
Coreless vortex
Cornell
Ketterle
ChapmanSengstock
Ho
Machida
Pu, Law
Bigelow
Ueda
Li You Ho,
Ueda
Ho+Mueller,
Cornell, Ueda
Cirac+Zoller, Ho+Mueller,Shouten+Read
Bloch, Fei Zhou, Yip, Delmer
Chapman
Sengstock
Stamper-
Kurn
Li You, Bigelow,
Bong, Sengstock
Bigelo
w
(Diener +Ho)
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Spin-1 and Spin-2 Bose Gases
Mean field description
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Statistical´ Ferromagnet, spin-gauge symmetry
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Na-23
Rb-87
c2
" 0
c2
0
antiferromagnetic
ferromagnetic
]Q "! (0,1,0) Polar phase
]Q "! 1,0,0 Quantum ferromagnet
Found at MITScience 1998
Bong,Sengstock, et.al. PRL 04, Chapman et.al PRL 04
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Spin 1
Ferromagnetic Antiferromagnetic
R
1
0
0
¨
ª
©©©
¸
º
¹¹¹
R
0
1
0
¨
ª
©©©
¸
º
¹¹¹
Vector order parameter
Spin-Gauge Symmetry
Nematic order parameter
Analogous phases seen in3
He
Similar to 2-component case
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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A x
! (a1
a1) / 2
A y
! (a1
a1) / 2i
A z
! a0
Define
Under spin rotation,
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Spin textures
Long sample
Short sample
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Single Skyrmion
components densityTexture
Ferromagnet
Low rotation speed
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Skyrmion pair Ferromagnet
Faster rotation speed
components densityTexture
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Skyrmion Lattice
Ferromagnet
Faster rotation speed
components densityTexture
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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AntiferromagnetAngular momentum carrying object:
-disclination or 1/2 vortex
ze| z|2
0
e
| z|2
¨
ª
©©©
¸
º
¹¹¹
Topological Singularity
Nematic order vanishes at core -- replaced with Ferromagnetic
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Single DisclinationOrder: pink=nematic
Green=ferromagnetic
Components
Density
Ferromagnetic
order
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Four DisclinationsOrder: pink=nematic
Green=ferromagnetic
Components
DensityCores aligned
antiferromagnetically
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Disclination LatticeOrder: pink=nematic
Green=ferromagnetic
Components
Density
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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Fast Rotating 2 componentMueller and Ho, PRL 88, 180403 (2002)
Triangle Skew Square StretchLocked
0 0.172 0.373 0.926
How lattices intermesh:
=Interaction between components
Interaction within components!
g 12
g 11 g 22
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Fast Rotating Spin-1/2 and Spin-1 Bose gas
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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L=2
L=4 L=12
Difference between
BEC and
quantum Hall state
BEC QH
N=2
N=4
Difficulty in stabilizing correlated states :
expansive in kinetic energy
Advantage: Zero potential energy
1 2
Vortex core 2
1
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New Quantum Hall systems:
Quantum Hall states with large spins
Bilayer (or Multilayer ) quantum Hall systems
Composite QH systems
Spin-1 Bose gas
scalar
scalar
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Density -- 5 particles
Total Density Component Densities
T.L. Ho and E. Mueller, PR L89, 050401 (2002)
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Optical Lattice:
A whole host of new states
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Effect of spin degeneracy on BEC
Only the lowest harmonic state is occupied
=> a zero dimensional problem
Spin-1 Bose Gas
Effect of spin degeneracy on BEC
A deep
harmonic
trap
aQ
Q!
1,0,1
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Spin-1 Bose Gas
Spin dynamics of spin-1 Bose gas
A deep
harmonic
trap
H ! c&S
2
Hilbert space
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Effect of spin degeneracy on BEC
Spin-1 Bose Gas
Effect of spin degeneracy on BEC
A deep
harmonic
trap
A x
! (a1
a1) / 2
A y
! (a1
a1) / 2i
A z
! a0
Under spin rotation, rotateslike a 3D Cartesean vector .
aQ p (ei
&
&S
a)Q
& A
ip R(
&)
ij
& A
j
R(&) : 3D rotation
aQ
Q!
1,0,1
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Effect of spin degeneracy on BEC
Spin-1 Bose Gas
Effect of spin degeneracy on BEC
A deep
harmonic
trap
N !a
Q
a
QQ§
&
S
!aQ
&
S QRaRQR
§
: spin-1 matrix
&S ! i
& A
v
& A N !
& A
& A
A x
! (a1
a1) / 2
A y
! (a1
a1) / 2i
A z
! a0
aQ
Q!
1,0,1
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Spin-1 Bose Gas
Effect of spin degeneracy on BEC
A deep
harmonic
trap
H ! c&S
2
&
S ! aQ &
S QR aRQR§
c " 0: Ferromagnetic ,
c 0 : Antiferromagnetic
H ! c N c(
&
A
)2&
A
2
What is the ground state for c>0 ?
8/3/2019 Jason Ho- Spinor-BEC and Multi-component Quantum Gases
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To find the optimal
spinor condensate ,
| ] "!( ^Q
Q§ aQ
) N
N !
| vac "
] | H | ] ! c&S
2
c N we minimize .
For c>0, diamagnetic case,
^ !
0
10
¨
ª
©
©©
¸
º
¹
¹¹
| ] "!
a0
N
N !| vac "!
( Ö z & A
) N
N !| vac "
&
S ! 0sincewe have
Since H is rotationally invariant, the optimal states are given by
; and
|] "!
( Ö n & A
) N
N !| vac " real.
Ö n ,the ³polar family´
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Conventional condensate :
| c "! a0 N | 0 " N !
aQ aR "! N
2
1
0
1
¨
ª©©©
¸
º¹¹¹
1 0 1
N 0 ! 0,
N s1 ! N /2
H ! c&S
2 C>0
&
S "! 0
( N 12 ~ N
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Exact ground state :
| S ! 0 "! 5 N /2 | 0 "
aQaR "! N
3
1 0 0
0 1 0
0 0 1
¨
ª©©©
¸
º¹¹¹
N 0 ! N 1 ! N 1 ! N / 3
H ! c&S
2 C>0
5 ! 2a1
a1
a0
2
( N 1
2~ N
2
=
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Average the coherrent state over
all directions
Relation between singlet state and coherent state
x
y
z
Because
( N 1
2~ N
2
The system is
easily damaged
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Transformation of singlet into coherent states as a function of
External field and field gradient:
If the total spin is non-zero
Bosonic enhancement
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Transformation of singlet into coherent states as a function of
External field and field gradient:
If the total spin is non-zero
Bosonic enhancement
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Transformation of singlet into coherent states as a function of
External field and field gradient:
If the total spin is non-zero
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Transformation of singlet into coherent states as a function of
External field and field gradient:
If the total spin is non-zero
With field gradient
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S/N
=/N^2
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Dynamical Evolution of
Spin-1 Bose Gas
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Spin-1 Bose Gas
Spin dynamics of spin-1 Bose gas
A deep
harmonic
trap
00
00
0
0
00
000
0
0 00
00
000 0
0
00 00
0000
0
0
0
0
Chapman et.al.
cond-mat/0309164
Watch how change with time
D i Ch l d /0309164
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Small fluctuation
Large fluctuationsOscillatory behavior in
t=0 starts here,
According to Chapman
Data in Chapman et.al. cond-mat/0309164
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To a large extent, can be explained by
time-dependent GP equation
What happen if one evolves the state properly by quantum mechanics?
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0.1% magnetizationLarge fluctuation
Oscillatory
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For simplicity, consider zero field
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is a sum of two theta functions !
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Relate to those at
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N=100
N=1000
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time
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Cr Condensate :
Tilman Pfau, PR L 2005.
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Dipolar coupling in fluids
Ferrofluids
~ 2-20 nm
Application:
rotary seals in disk drives
dampers for audio speakers
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Cond-mat/ Nov 2005
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Signiture of Quantum dynamics:
(1) Complete revival
(2) Periodic variation between cat states and coherent states
(3) Entire spacetime structure is control by scaling
(4) Printing of phase can be deprint at later time
(5) Can be detected by population histogram at time p/q
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What have we learned ?
What novel things awaiting for us?
What can we do with multi-component
Bose gases?
What is new?
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What have we learned ?
What novel things awaiting for us?
What can we do with multi-component
Bose gases?
What is new?
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Periodic changes from coherent state toSchrodinger Cat state
Can introduce phase difference between difference component
of the Cat, and retrieve those information later.
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Question: What really new things BEC
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Question: What really new things BEC
has brought us?
Ans: Bose gas with internal degrees
of freedom --Pseudo-spin 1/2 Bose gas,
Spin-1 and Spin-2 Bose gas
New ground states, a whole host of newquantum phenomena, forces on to re-
examine BEC with greater depth
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Work done with
Dr. Roberto Diener Prof. S.K. Yip
Work supported by NSF and NASA
Tin-Lun Ho and Sung Kit Yip,Physical Review Letters 84,
4031 (2000)
R. Diener and Tin-Lun Ho, to be published
´ !2« »
Single component
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H ! ´ !2
2 M ] ] V (
&r )]]
g
2](r )](r )](r )] (r )
«
-¬»
½¼
H ! ´ !2
2 M ]Q
]Q V (r )]Q]Q
1
2 g QR]Q
]R]R]Q
«
-¬»
½¼
Q !o,q
H s
!!
2
2 M ]
Q]
QV (
&r )]
Q]
Q K
& B ]
Q & F QR
]R
«
-¬¬
»
½¼¼
1
2c
0]Q]
E]
E]Q c
2]Q]
E & F QR
& F EF
]F]R
«-¬
»½¼´́
L]Q ( Ö B
& F )
2«-¬
»½¼QR
]R
´
+
Two component
Spin-1
T.L. Ho, PR L (98), K . Machida et.al J. Phil Mag (98)
T.L. Ho, PR L 87, 81, 742 (1998)
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f = 1
N a23
, K 39
Rb87
V (1,2) ! H(&
r 1
&
r 2) c
01 c
2
&
F 1
&
F 2
c0
! (2 g 2 g 0) /3,
c2
! ( g 2 g 0) /3,
Na-23
Rb-87
c2
" 0
c2 0
antiferromagnetic
ferromagnetic
It is useful to rewrite P in terms of spin operators
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It is useful to rewrite P in terms of spin operators.
1! P 0 P
2
2&
F 1
&
F 2
! § F ! 0
2 f F ( F 1) Ö P
f 2 f ( f 1)Ö 1
2&
F 1
&
F 2
! (&
F 1
&
F 2)2
&
F 12
&
F 22
&
F 1
2!
&
F 2
2! f ( f 1)
2&
F 1
&
F 2
! 6 Ö P 2 2 Ö P
1 4( Ö P
2 Ö P
1 Ö P
0)
&
F 1
&
F 2
! 2 Ö P 2 2 Ö P
0
1! P 0 P
1 P 2
V (1,2) ! H(&
r 1
&
r 2) g
0 P
0 g
2 P
2 ! H(&
r 1
&
r 2) c
01 c
2
&
F 1
&
F 2
c0
! (2 g 2 g
0) /3, c
2! ( g
2 g
0) /3,
23 39 87
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f = 1
N a23
, K 39
Rb87
f = 2
Rb83
Rb85
C s133,C s135,C s137f = 3
V (1,2) ! H(&
r 1
&
r 2) c
01 c
2
&
F 1
&
F 2
V (1,2) ! H(&
r 1
&
r 2) c
01 c
2
&
F 1
&
F 2 c
4(&
F 1
&
F 2)2
V (1,2) ! H(&
r 1
&
r 2) c
01 c
2
&
F 1
&
F 2 c
4(&
F 1
&
F 2)2 c
6(&
F 1
&
F 2)3
86.2days
30.2yrs3Million yrs
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Fragmented vs Coherent Condensates
Can there be other possibilities ?
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Can there be other possibilities ?
PE
E
0
1
2
3
P0
~ N
P1
,P2
,...~O(1)
PE
E0 1 2 3
P0
,P1,P
2,...~O(1)
Fragmented condensate
Various states of light:
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Coherent
(Gaussian)
State
Squeezed
State
Cat State
Bosons in double well:
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1 2Bose gas in double well <==> A simple model of
B
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t
1 2two component Bose gas
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Zero
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The Ground States of
Zero Dimensional Spin-1 Bose Gas
S
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S
singlet
Squeezed
coherent
Field gradient
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Quantum carpet for a particle in a box
M V Berry Quantum fractals in boxesJ. Phys. A 29 6617-6629 (1996)
C Leichtle, I S Averbukh and W P Schleich 1996 Multilevel quantum beats: an analytical approachPhys. Rev. A 54 5299-312 (1996)
O Friesch, I Marzoli and W P SchleichQuantum carpets woven by Wigner functions
N ew J. Phys. 2, 4.1-4.11 (2000)
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Many simple questions have
led us to remarkable surprises Nature has for us
0.2% magnetization
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0.2% magnetization
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g
Note: According to mean field, if all bosons are
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Our approach: Quantum evolution of the initial state
g ,
initially in the state, should
remain constant, .
within the single mode approximation.
Key findings:
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y g
1. Find all the features observed in expt.
2. Obtain an analytic solution for the time evolution
of the wavefunction.
3. The exact solution reveals many additional
revival features at longer times
4. Our exact solution is also applicable to the studiesof ³quantum carpets´ in the last decade in atomic
and molecular physics. It is a concise summary
of all numerical results in the last decade.
More details of our approach:
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A. We note that single mode approximation is valid in this case.
Hence
B. Different spin component of a quantum state will dephase
over time . Beyond this time, mean field approach is
no longer valid.
C. The general quantum state for is
Schrodinger Cat running on a Quantum Carpet:
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The large fluctuation is due to dynamical fragmentation of the
condensate -- a periodic transformation between Schrodinger
Cat state and a coherent state.
Schrodinger Cat state occurs at ct = coherent state
occurs at ct =
Phase imprinting at pi/8 (using quadratic Zeeman effect) will affect
subsequent time evolution, and will change the coherent state
structure.
Deprinting the phase at 3\pi/8 can restore the original time evolution
Reference:
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(a) Roberto Diener and Tin-Lun Ho, to be published.
( b) M.-S. Chang, C.D. Hamley, M. D. Barrett, J.A. Sauer,
K.M. Fortier, W. Zhang, L. You, M.S. Chapman,
cond-mat/0309164.
(c) Schmaljohann, M. Erhard, J. Kronjäger, M. Kottke,
S. van Staa, L. Cacciapuoti, J. J. Arlt, K. Bongs, and K. Sengstock
Phys. Rev. Lett. 92, 040402 (2004)
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N o as a function of time without magnetization
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N_o as a function of time, without magnetization,
with magnetization, etc.
Phase impriting
M=10, N=1000
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non-zero q, q=0.1Initial state : N_{o}=N, M=0
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We have only talked about 3/5 of the major development
last year
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last year.
Two other major developments:
*Spin-1 and Spin-2 Bose gas:
Expt. (Chapman) (Sengstock )
=> Quantum dynamics of
Spinor BEC and Superfragmented condensates
=> Periodic generation of Schrodinger Cat state
Low dimensional quantum gases
T.L.Ho, PRL, 81, 742 (1998)
T.L. Ho and S.K. Yip,PRL 84, 4031(2000)