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2 new very accurate determinations of the s-wave scattering length in metastable helium. Steven Moal, Maximilien Portier, Julien Dugué, Christian Buggle, Nassim Zahzam, Michèle Leduc, Claude Cohen-Tannoudji. séminaire Atomes-froids vendredi 28 octobre 2005. Study with 1 photon :

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slide1

2 new very accurate determinations of the s-wave scatteringlengthin metastable helium

Steven Moal, Maximilien Portier, Julien Dugué,

Christian Buggle, Nassim Zahzam,

Michèle Leduc, Claude Cohen-Tannoudji

séminaire Atomes-froids vendredi 28 octobre 2005

slide2

Study with 1 photon :

Frequency shifts of photoassociative spectra

slide3

Principle of experiment

23PJ

1083

nm

He*

23S1

~19.8 eV

 ~ 2 h

11S0

0u+

E

S + P0

Ev = 0 (,I)

Energy

5 g+

continuum

kBT

S + S

r

v=14

R

Interatomic distance

slide4

Principle of experiment

E

E

c

o

n

t

i

n

u

u

m

dressed atom picture

0u+

5 g+

S + P0

continuum

Ev = 0

v=0

E=kBT

kBT

0

r

S + S+ ħ 

v=14

Ev = 14

R

slide5

Experimental result

E

0u+

S + P0

v=2

v=1

v=0

R

From comparison

with theory

Our value :

a = 7.2 ± 0.5 nm

slide6

Study with 2 photons :

Dark atom-molecule resonances

Mesure of lifetime and position of v=14

slide7

2 photon spectroscopy

E

0u+

S + P0

v = 0

2

1

Energy

5 g+

S + S

r

v=14

R

Interatomic distance

slide8

From Autler-Townes to Raman effect

E

E

E

v = 0

v = 0

v = 0

1

  • 2

fixed

  • 2

fixed

1

scanned

 2

1

scanned

1

v=14

2

v=14

v=14

R

R

R

slide9

From Autler-Townes to dark resonance

100 µW in 2nd photon

3 mW in 2nd photon

500 µW in 2nd photon

100 µW in 2nd photon

1 mW in 2nd photon

300 µW in 2nd photon

slide11

From Autler-Townes to dark resonance

0u+

E

S + P0

v=0

2

1

Energy

5 g+

continuum

kBT

S + S

r~ -90 MHz

v=14

R

Interatomic distance

slide12

From Autler-Townes to dark resonance

100 µW in 2nd photon

30 µW in 2nd photon

100 µW in 2nd photon

10 µW in 2nd photon

3 µW in 2nd photon

slide13

Dark resonance

E

S–P0

v = 0

  • 2

1

free atoms

S–S

v=14

R

destructive interference between the absorption amplitude of

photon 1 on the free / bound v=0 transition

and of

photon 2 on the bound v=0 / bound v=14 transition

slide14

Mesure of Ev=14

E

S + P0

v=0

 2

1

kBT

S + S

v=14

r

R

shift du to T : 3kBT/2

experimentally we have 15 % less

no need of the

energy of v=0

Position of v=14

-91.35 ± 0.06 MHz

slide15

Scattering length

New value :

a = 7.512 ± 0.005 nm

slide16

Theoretical values

Other results

IOTA 2001

a=20±10 nm

Stark and Meyer 1994

a=8 nm

ENS 2001 a=16±8 nm

ENS 2002 a<16 nm

Gadéa, Dickinson and Leininger 2004

8.0<a<12.2 nm

VU 2004 a=10±5 nm

Przybytek and Jeziorski 2005

a=7.64±0.20 nm

IOTA 2004 10.3<a<13.8 nm

2 photons

Light shift

x 200

7.507

7.517

0

5

10

15

20

25

30

a (nm)

slide17

Mesure of lifetime v=14

v=14 has not a infinite life duration

the dark resonance doesn’t go to 0 at weak intensity

0.05 < v=14 /2 < 0.3 MHz

0.5 < v=14 /2 < 3 µs

Rough estimate : 4 µs

from Penning collision rate between two polarized atoms

Kinel = 3.10-14 cm3 s-1

(Fedichev and Shlyapnikov, 1996)

2 µW in 2nd photon

1 µW in 2nd photon

0.5 µW in 2nd photon

5 µW in 2nd photon

4 µW in 2nd photon

3 µW in 2nd photon

slide18

Conclusion

  • 2 very accurate (and different) measurements
  • of the scattering length :
  • with frequency shift : a = 7.2 ± 0.5 nm
  • with dark resonance : a = 7.512 ± 0.005 nm
  • Creation of exotic molecules of 2 metastables
  • with inhibited autoionisation with
  • a lifeduration of 0.5 < v=14 /2 < 3 µs
slide19

Soon

  • influence of density on v=14
  • a better value for v=14 with the study of Raman signal :
    • in fonction of temperature
    • in fonction of the detuning
  • position and width of v=14
  • in the potential S-S (M=0)
  • study of the 2 photons signal
  • during the transition
  • thermal cloud / BEC

E

S-P0

v = 0

2 , +

1 , -

S-S MJ=2

v=14

2µB0

S-S MJ=0

v=14

R

slide21

Other experiments

Grimm, Innsbrück, April 2005

in 87Rb BEC

PRL 95, 063202 (2005)

  • lifetime on
  • the dark resonance is 140 ms
  • 100 molecules Rb2
slide22

Other experiments

Lett, NIST, July 2005

in 23Na dark MOT

PRA 72, 041801R 2005

  • dip width around 5 MHz du to :
  • thermal energy distribution at T=150 µK, kBT/h~3 MHz
  • intensity of 2nd photon kept high
slide24

Principle of experiment

1.4 GHz

280 THz1083 nm

30 000 GHz

=0.5 MHz

slide25

Raman effect

Raman pic in the red of the main line.

 = -10 MHz

But the main line can be shifted.

 = -30 MHz

Raman pic in the blue of the main line.

 = few MHz

slide26

Mesure of PA rate transition ?

PA = 10 ms

Therm = 400 ms

PA = 1 ms

Therm = 200 ms

PA = 2 ms

Therm = 100 ms

PA = 5 ms

Therm = 50 ms

PA = 10 ms

PA = 1 ms

PA = 10 ms

PA = 2 ms

PA = 5 ms

Therm = 400 ms

PA = 1 ms

a clear signal in the Number of atom for Therm = 0 ms

we have information on PA rate transition

Therm = 0 ms

slide27

Black resonance

10 µW.cm-2 in 2nd photon

1 µW.cm-2 in 2nd photon

slide28

séminaire du

vendredi 10/06/05

Pour bientôt :

MJ=0

s +

MJ=2

s -

E

Ev=0

0

Ev=14

Ev=14

slide29

E

E

0u+

5 g+

S + P0

kBT

v=0

continuum

r

S + S + ħ 

v=14

R