Transcript COLD_MOLECULES_AND_SPECTROSCOPY_Ohio_2008.ppt

Leibniz Universität
Hannover
COLD MOLECULES AND SPECTROSCOPY:
A CHALLENGE AND NEW CHANCES
E. TIEMANN, H. KNÖCKEL, and C. LISDAT, Hannover
A. PASHOV, Sofia
M. TAMANIS, R. FERBER, Riga
DFG
Production of cold molecules
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translationally and/or internally
• cold atoms 
•
•
•
•
photo association
coherent transfer to
other quantum states
Feshbach spectroscopy
selecting cold molecules out of a thermal ensemble
decelerating a bunch of molecules
ground state
cooling molecules by coupling dissipative channels
molecules
(e.g. cavity mode)
buffer gas cooling, sympathetic cooling
• combination of different cooling steps to reach ultra cold regime
spectroscopic data applied at almost all stages
- to model or predict the needed physical conditions
- to observe the prepared cold ensemble
- to initiate new processes
Initial conditions for free molecules
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center of mass motion
fast
hot ensemble
molecular beam
near zero velocity
cold ensemble
• spectroscopy of
• photoassociation
“normal” molecules
• cold collisions and
• coherent manipulation to get
Feshbach resonance
• decelerated bunches, …
pairs of distant atoms
• coherent manipulation to
 long range interactions
“normal” molecules
• cold collision spectroscopy
or desired quantum state
Complementary results
Potential scheme of alkali dimers
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example NaRb (Korek et al 2000)
entrance channel
cold
high resolution Fourier spectroscopy
spectroscopy entrance
hot
Spectroscopy of cold collisions
Spectroscopic situation
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Hund‘s case c coupling
Fourier spectroscopy for wide range
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NaRb
A. Pashov et al., Phys. Rev. A 72, 062505 (2005)
Progression to state a3S+ and X1S+
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NaRb
precise
energy differences
hyperfine splitting
example K2
two-photon excitation for u states
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fluorescence from the (v‘ = 6, J‘ = 29) rovibrational level of the state 2 3Pg
A. Pashov, P. Popov, H. Knöckel, E. Tiemann, Eur. Phys. J. D 46, 241 (2008)
Hamiltonian of electronic system
for ns + n’s asymptote
singlet state
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triplet state
H  Tn  U X ( R) PX  U a ( R)(1  PX )
adiabatic potentials
 
 
 a A ( R) s AiA  aB ( R) sB iB
hyperfine interaction
 ( g sAs zA  g iAizA )  B Bz  ( g sB s zB  g iBizB )  B Bz
Zeeman interaction
2
  ( R)(3S  S )
2
3
2
Z
molecular axis
spin-spin interaction
space fixed axis
Construction of the adiabatic ground state potentials
inner part R (s)
i
Ri (t)
Ro(t,s)
Vs / t ( R)  As / t  Cs / t / R n
V R   
6000
energy (cm-1)
long range part
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C6 C8

   Eex
R 6 R8
Eex R   Aex  R   e  Bex R
continuous &
@transition Ri
3000
fit to exp. data:
V(R) = + a1x + a2x2 + a3x3 + ...  D
RR
x (R,b) = R + bRm
m
0
1
evaluation
2
4
6
8 10
R(Å)
20
40
60
Mass scaling the vibrational ladder?
example 7LiK and 6LiK for X1S+
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combined analysis
of X1S+ and a3S+
for 6/7Li39/41K
from spectroscopy
and
Feshbach resonances
for 6Li40K
data from PhD thesis Houssam SALAMI,
Univ. Lyon 2006
E. Wille et al, PRL 100, 053201 (2008)
gap between data of
Fourier transform spectroscopy
Feshbach resonances
modified Schrödinger equation for BO corrections
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 PR2

me A
me B
 U n R  
U ad R  
U ad R   

MA
MB
 2

 P 2
  nl  Enl  nl
 R

me
me
A
B
 J ( J  1) 1  M A U nad ( R)  M B U nad ( R) 


2
2 R




rotational dependence
full application on I2 with 127I2 and 127I129I for an excited state
first results on 6/7Li39K from spectroscopy
first indications for 39K2 and 40K2 from spectroscopy and cold collisions
KRb also?
energy (cm -1)
Excitation scheme for pair spectroscopy
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4s + 4p
v´= 143...159, J´
16000
1
A S +u
12000
v´= 23
L2
8000
L3
L1
X S +g
1
4000
4s + 4s
v´´ = 80...83
v´´= 41
v´´= 0
0
2
setup
3
4
5
6
7
8
9
10
11
R
asymptotic rovibrational structure in the A state
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dissociation continuum
Study of 39K2 and 39K41K  deviation of Born-Oppenheimer approximation in A state
asymptotically in ground state?
S. Falke et al., J. Chem. Phys. 125, 224303 (2006)
and Phys. Rev A 76, 012724 (2007)
Examples of observed dark resonances
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coherent L-scheme L2+L3
hyperfine splitting
fluorescence
I=3
I=1
L3 R(7) 143-80
L2 R(7) 143-41
L3 R(5) 159-83
L2 P(7) 159-41
20MHz
rel. frequency to P(72) 0-14 a1 (MHz)
rel. frequency to R(102) 1-14 a1 (MHz)
Analysis of all K2 isotopes including Feshbach resonances for 40K and 39K
 first hint of isotope shifts of the resonances in the order of 1G
 limit of applicability of mass scaling for cold collisions
S. Falke et al, PRA in press
scattering resonances: Na (3s) + Na (3s) asymptote
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hyperfine potentials (C6/R6 subtracted)
f1+f2
f=4
2+2
asymptote
experimental signal
threshold
f=2
f=0
asymptote
1+1
shape resonance
asymptote
M. Elbs et al., Phys. Rev. A 59, 3665 (1999)
l=0
f=2
detection by
fluorescence
from
vA = 139, J=1
v = 65
X l=2
f=0,2
X v =65
bound
f=0
l even
Feshbach resonance
Feshbach resonance
f=2
f=2
l=2
f=2
1+2
l,=0f=2
0.8
f=1,3
1.0
a
C. Samuelis et al., Phys. Rev. A 63, 012710 (2001)
Cold molecules and cold chemistry
collisions Cs2 + Cs  relaxation
resonance structure in Cs2 + Cs2  Cs4 (Feshbach molecules)
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Freiburg, Orsay
Innsbruck
“free” choice of molecules desirable  applying “all” types of molecule production
cold atoms  photoassociation, Feshbach molecules
buffer gas cooling or sympathetic cooling
selecting slow molecules
deceleration of molecules
reaction kinetics
photodissociation
Cold photodissociation
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J N
b
634
3 2
a
2 1
a
625
excited SO2
~1
C B2(1,4,2)
1 0
0 1
b
SO (v = 0)
+O
continuum
production of cold fragments: SO2 as a possibility
S. Becker et al, Chem. Phys. 196, 275 (1995)
Stark deceleration of SO2
Experimental setup
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decelerator
hexapole
skimmer
pulsed nozzle
1. beam generation by a pulsed valve
2. geometrical cooling by a skimmer
3. hexapole to achieve phase
matching of beam and decelerator
4. Stark decelerator for low-field
seeking states
5. time of flight measurements
Switching electric fields
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+
beam

2L
decelerating
Switching electric fields
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+
+


beam
DE
2L
guiding
decelerating
Slow SO2
short decelerator
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TOF spectrum
 = 55°
U = 12.5 kV
deceleration from
285 m/s to 217 m/s
42% of kin. energy
SO2
guiding 317 m/s
111 |M| = 0
Monte Carlo
simulation
bare beam
2.4
2.6
2.8
3.0
3.2
3.4
3.6
flight time (ms)
3.8
4.0
4.2
4.4
Decelerator with 326 stages
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low velocity 53m/s  trappable bunch of SO2
O. Bucicov et al, EPJD DOI: 10.1140/epjd/e2008-00001-y
“pure” internal quantum state
populated v=(0,0,0) 111
exit of
decelerator
entrance of
decelerator
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Stark effect and dissociation
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manipulation
cold
SO2
variation of
 kinetic energy
 population of quantum states
continuum for fragments
SO + O
electric plus magnetic fields: R. V. Krems, Phys. Rev. Lett. 96, 123202 (2006)
Tuning the dissociation
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48000
M=0
M=0
M=1
M=2
M=3
47998
3(1,3)
47997
2(1,2)
47996
1(1,0)
SO2 (510) J(K -,K +)
SO v = 2 (N,J) + O 3P2
thresholds
47995
-1
term energy (cm )
47999
(2,3)
1(0,1)
47994
SO and O both in
triplet states
47993
47992
(1,2)
electric and magnetic traps
for fragments
 accumulation of cycles
 photo association ?
47991
47990
(0,1)
47989
(1,0)
47988
0
50
100
150
electric field (kV/cm)
200
Conclusions
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• joining Feshbach spectroscopy and molecular spectroscopy
precise modeling of simple systems  extending to high multiplicity?
• limits of mass scaling for cold collisions become visible
studied in our groups: Na2, K2, LiK, LiRb, LiCs, NaK, NaRb, NaCs, KRb, KCs, Ca2, Sr2
• next: high precision spectroscopy of ground states of cold molecules
• precise study of mechanics and the constancy of mass ratios
• electric dipole moment of the electron?
• cold chemistry: alkalis,…, OH, NH3, H2CO, SO2, …
• coherent chemistry by matter waves or superposition of quantum states
 studying the conical intersections?
• modeling ultracold ensembles with composite particles
 “ideal” condensed matter physics
DFG
Spectrum for state a3S+ with hyperfine structure
Rb
Na
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experimental setup
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Hannover
K/K2
to stabilization
L2+L3
Verdi
Ti:Sa laser
single
mode
fiber
800 nm
Verdi
Ti:Sa laser
710 nm
diode laser
792 nm
L1
single mode fiber
Franck-Condon
pumping
oven
to stabilization
Diagram of Evaluation
Feshbach resonances
from cold collisions
data of X-state
data of a-state
single channel
potential fit
single channel
potential fit
coupled channel calculation
with atomic hyperfine parameters
corrections from
channel coupling
Convergence to coupled system of
3 +
1 +
X S and a S
prediction of cold collision properties:
Feshbach resonances, scattering lengths
also for isotopomers
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common asymptote
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Stark deceleration of SO2
force in inhomogeneous fields
6.0
5.0
211
Energie [cm-1]
energy
4.0
3.0 1
11
2.0
202
1.0
0.0
000
|M|= 0
|M|= 1
|M|= 2
-1.0
-2.0
-3.0
0
50
100
fieldFeldstärke
strength [kV/cm]
150
200