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Coherent processes in metastable helium at
room temperature
Thomas LauprêtreFabienne GoldfarbFabien Bretenaker
Laboratoire Aimé Cotton, Orsay, France
School of Physical Sciences, Jawaharlal Nehru University, Delhi, India
Rupamanjari GhoshSantosh Kumar
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Summary
• Electromagnetically Induced Transparency
• Experimental set-up• Dispersion in a cavity• Tripod system
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Electromagnetically Induced Transparency ?
• Fact:Optical transition is made transparent for
a resonant field (otherwise opaque medium)
• How it happens:A quantum interference effect, induced by
a control field on a second transition
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cp c
One optical transitionΛ system
ab
cR 2
22
p
Rc b
a
ab
Electromagnetically Induced Transparency (EIT)
Width of transparency window
R
cbR
relax
cb
t
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EIT and Slow Light
• Kramers-Kronig
Strong positive dispersion
d
dn
cvg )Re(
2
Slow Light !
Kash & al, PRL, 1999: 90 m.s-1 in RbHau & al, Nautre, 1999: 17 m.s-1 in cold Na
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Summary
• EIT• Experimental set-up• Dispersion in a cavity• Tripod system
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Metastable 4He
1S0
3P1
3S1
m = -1 10
RF discharge
p p
0
12
c
c
• Lifetime ~8000s
polarization selected Λ system
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Experimental results
D
cR W2
22
W
idth
at
ha
lf m
ax
imu
m (
kH
z)
Coupling intensity (W.m-2)
Gro
up
de
lay
(µs
)
Coupling intensity (W.m-2)
Group velocity around 8 km.s-1 !Goldfarb, F. & al.,
EPL (Europhysics Letters), 2008, 82, 54002
Ghosh, J. & al., Phys.Rev.A, 2009
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Summary
• EIT• Experimental set-up• Dispersion in a cavity• Tripod system
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Dispersion in cavity• Why?
Enhance sensitivity of cavity based sensors (ring laser gyroscope…)
Positive dispersion reduces the linewidth of a resonator
• Main parameter: lifetime of photons in the cavity
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Lifetime of photons
• 2 different points of view
1) Phase velocity Resonant cavity:monochromatic field
2) Group velocityGaussian pulseΔt ∞ ?
Δt
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Experiment
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Global results
• Measured decay time ~ a few µs • ~150 ns with phase velocity
Group velocity !
τcav
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Summary
• EIT• Experimental set-up• Dispersion in a cavity• Tripod system
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Tripod system
1S0
3P0
3S1
RF discharge
m = -1 10
Santosh Kumar, School of Physical Sciences, Jawaharlal Nehru University, Delhi, India
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Tripod system
ΩP ΩPΩC
my = -1 10
0
B
(kHz)
ΩC ΩCΩP
my = -1 10
0
B
B
Laser
π
σ
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Outlook
• Negative dispersion inside our cavityFast lightNegative group velocity
• Further investigations on Tripod system
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0<vg <c c<vg vg <-c -c<vg <0
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