carsten klempt et al- direct observation of vacuum fluctuations in spinor bose-einstein condensates
TRANSCRIPT
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
1/33
Direct observation
of vacuum fluctuations
in spinor
Bose-Einstein
condensates
Carsten Klempt, Oliver Topic, Manuel Scherer,Thorsten Henninger, Wolfgang Ertmer, and Jan ArltInstitute of Quantum Optics
Gebremedhn Gebreyesus, Philipp Hyllus, and Luis SantosInstitute of Theoretical Physics
of
in
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
2/33
Vacuum fluctuations in spinor BECs
Introduction
Nonlinear crystal
Optical spontaneous parametric down-conversion
pair creation parametric
amplification
amplification ofvacuum
fluctuations
entangled pairs (EPR)
squeezing
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
3/33
Vacuum fluctuations in spinor BECs
Spinor BECs
Confined spinor BECs
Vacuum fluctuations
Introduction
Contents
Experiments
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
4/33
Vacuum fluctuations in spinor BECs
Spinor BECs
Confined spinor BECs
Vacuum fluctuations
Introduction
Contents
Experiments
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
5/33
Vacuum fluctuations in spinor BECs
Atoms with non-zero spin
Spinor gases:
Alkali-atoms
with non-zero spin
Here:
87Rb F=2 mF=0
E= p m + q m2
p ~ B
q ~ B2
< 0
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
6/33
Vacuum fluctuations in spinor BECs
Energy scales
Competing energy scales define the ground state
mF=0
mF=1
Repulsive interaction
quadratic Zeeman energy interaction energy
mF=0
mF=1
Attractive interaction
quadratic Zeeman effect
interactions
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
7/33
Vacuum fluctuations in spinor BECs
Ground states of spinor BECs
H. Schmaljohann et al., PRL 92, 040402 (2004).
Ground states ofF =2 Spinor Bose-Einstein Condensates
Ciobanu et al., PRL 61, 033607 (2000).
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
8/33
Vacuum fluctuations in spinor BECs
Spinor BEC in F=2, mF=0
( ) ( ) ( ) ( )
( )( )( )( )
( )
+
=+=
+
+
r
r
r
r
r
rrrr
r
r
r
r
r
rrrrrrr
2
1
0
1
2
00
0
0
0
0
( ) ( ) ( ) ( )rrUrVM
rrrrhr
0
2
000
22
02
++
=
Condensate Excitations
Scalar Gross-Pitaevskii equation for m=0
Field operator for the spinor BEC in F=2 mF=0
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
9/33
Vacuum fluctuations in spinor BECs
Hamiltonian for spin excitations
( )[ ]( )[ ]
++
+
=
+
+=
+
1111
1
3
r
qrH
rdHeff
m
meffm
r
r
( ) ( )rnUreffrr
011
Hamiltonian (linear regime)
( ) ( ) ( ) ( ) +++
rnUUrVMrHeff
rrhr01100
22
2
Veff
Veff
Spin changing collisions
This Hamiltonian describes the time evolution of the mF=1 components
homogeneous case
mF=0
Identical to optical parametric amplification !
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
10/33
Vacuum fluctuations in spinor BECs
Spin Bogoliubov modes
2 possibilities [Lamacraft, PRL 98, 160404 (2007)]
1) Real Eigenvalues: system is stable
no population in mF=1
2) Complex Eigenvalues: system is unstable
Eigenmodes of the Hamiltonian
are Spin Bogoliubov modes in mF=1with wavevector k
which are exponentially amplified: e2 Im(E) t
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
11/33
Vacuum fluctuations in spinor BECs
Stability diagram (homogeneous)
q>0
stable
qcr
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
12/33
Vacuum fluctuations in spinor BECs
Measurements on homogeneous system
87Rb F=1
Creation of spatial structure (broken symmetry)Sadler et al., Nature443, 312 (2006)
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
13/33
Vacuum fluctuations in spinor BECs
Spinor BECs
Confined spinor BECs
Vacuum fluctuations
Introduction
Contents
Experiments
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
14/33
Vacuum fluctuations in spinor BECs
Confined case
What changes when weconsider the trapping potential ?
quadratic Zeeman effect
interactions
confinement
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
15/33
Vacuum fluctuations in spinor BECs
Hamiltonian for spin excitations
( )[ ]( )[ ]
++
+
=
+
+=
+
1111
1
3
r
qrH
rdHeff
m
meffm
r
r
( ) ( )rnUreffrr
011
Hamiltonian (linear regime)
( ) ( ) ( ) ( ) +++
rnUUrVMrHeff
rrhr01100
22
2
Veff
Veff
This Hamiltonian describes the time evolution of the mF=1 components
confined case
mF=0
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
16/33
Vacuum fluctuations in spinor BECs
Spin Bogoliubov modes
2 possibilities
1) Real Eigenvalues: System is stable
no population in mF=1
2) Complex Eigenvalues: System is unstable
Eigenfunctions of the Hamiltonian
are Spin Bogoliubov modes in mF=1composed of the eigenstates of the eff. Potential
which are exponentially amplified
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
17/33
Vacuum fluctuations in spinor BECs
Stability diagram (homogeneous)
q>0
stable
qcr
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
18/33
Vacuum fluctuations in spinor BECs
Spinor BECs
Confined spinor BECs
Vacuum fluctuations
Introduction
Contents
Experiments
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
19/33
Vacuum fluctuations in spinor BECs
Experimental setup
Dispenser
MOT cell(10-9 mBar) science cell
(< 10-11 mBar)
differentialpumping stage
LIAD: an efficient, switchable atom sourceC. K., T. van Zoest, T. Henninger, O. Topic, E. Rasel, W. Ertmer und J. Arlt, Phys. Rev. A 73, 13410 (2006).
4109 atomsat 45 K
87Rbmolasses
40Kmolasses
5107 atomsat 260 K
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
20/33
Vacuum fluctuations in spinor BECs
Optical dipole trap
Optical dipole trap ( =1064 nm, 2 W)whorizontal = 25 m, wvertical = 60 m
T = 1,0 K
center of coils:(100 Hz / 15 Hz)
6 106 87Rb-atoms
3 106 40K-atoms
4 106 87Rb-atoms
2 106 40K-atoms
T = 1,5 K
dipole trap(370 Hz / 170 Hz)
transfer
evaporation
3 105 87Rb-atoms
3 105 40K-atoms
T = 270 nK
B = 8 mG @ 550 G
B = 4 mG @ 1 G
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
21/33
Vacuum fluctuations in spinor BECs
F=2
mF=-1
mF=0
mF=2
mF=1
mF=-2
78 80 82 84 86
-8
-6
-4
-2
0
2
4
6
8
Energyofc
oupledsystem[
MHz]
Radiofrequency [MHz]
Radio frequency
sweep in 1ms
78 Mhz 82 MHz
B-Field=120G
mF
= -1
mF=0
mF=2
mF
=1
mF= -2
mF=1
mF=0
mF= -2
mF
= -1
mF=2
Spin preparation
87Rb
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
22/33
Vacuum fluctuations in spinor BECs
Hold time with
magn. field
Stern-Gerlach and
detection
mF=0 preparationat 120 G
297.5mG 395mG 512mG 570.5mG
x=46Hz
y=132Hz
z=176Hz
NBEC
=4x104
thold=21ms
Measuring sequence
Purification:strong gradient
0
-1
+1
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
23/33
Vacuum fluctuations in spinor BECs
Spin dynamics resonances
exp
theory
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
24/33
Vacuum fluctuations in spinor BECs
Ground state and excited states
1st Resonance 2nd Resonance
mF=1
mF=0
mF=-1
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
25/33
Vacuum fluctuations in spinor BECs
Spinor BECs
Confined spinor BECs
Vacuum fluctuations
Introduction
Contents
Experiments
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
26/33
Vacuum fluctuations in spinor BECs
Triggering of spinor dynamics
2 possibilities
1) System is stable
no population in mF=1
2) System is unstable
Eigenfunctions of the Hamiltonian
are Spin Bogoliubov modes in mF=1composed of the eigenstates of the eff. Potential
which are exponentially amplified
What triggers
the spinor dynamics ?
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
27/33
Vacuum fluctuations in spinor BECs
Seed
2 possibilities
1) Spurious radiofrequencies or magnetic field noise
produce atoms in mF=1 in the spatial mode of the
initial BEC classical seed
2) No atoms present in mF=1 vacuum fluctuations
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
28/33
Vacuum fluctuations in spinor BECs
Experimental verification
exp
theory
Produce a classical seeddeliberately:
Radio-frequency pulsewith extreme small amplitudecouples the BEC in mF=0symmetricallyto the states mF=1
(after purification)
V fl t ti i i BEC
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
29/33
Vacuum fluctuations in spinor BECs
Classical vs quantum seed
exp
theory
classical
seed
vacuum
fluctuations
V fl t ti i i BEC
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
30/33
Vacuum fluctuations in spinor BECs
Amplification of classical and quantum seed
classical fluctuations vacuum fluctuations
mF=1
mF=0
mF=-1
Vacuum fluctuations in spinor BECs
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
31/33
Vacuum fluctuations in spinor BECs
Overlap of classical seed
How relevant is the classical seed ?
Vacuum fluctuations in spinor BECs
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
32/33
Vacuum fluctuations in spinor BECs
Outlook
Analyze spatial structurequantitatively
Quantify fluctuations
Demonstrate squeezing(measure quadratures)
Extract EPR pairs ? Investigate effects ofdipolar interaction
Vacuum fluctuations in spinor BECs
-
8/3/2019 Carsten Klempt et al- Direct observation of vacuum fluctuations in spinor Bose-Einstein condensates
33/33
Vacuum fluctuations in spinor BECs
People
Carsten Klempt, Oliver Topic, ManuelScherer, Thorsten Henninger, WolfgangErtmer, and Jan ArltInstitute of Quantum Optics
Gebremedhn Gebreyesus, Philipp Hyllus,and Luis Santos
Institute of Theoretical Physics