Observation of Quantum Observation of Quantum CoherenceCoherence
for Gaseous Moleculesfor Gaseous Molecules
Jian Tang (唐 健)Natural Science and Technology (Chemistry)
Okayama University
FPUA2010FPUA2010 Aug. 7-9, Osaka Univ.Aug. 7-9, Osaka Univ.
Collaborators
Okayama Univ. (Chemistry) Okayama Univ. (Physics)
Y. Okabayashi (岡林祐介) K. Nakajima (中島享)
Y. Miyamoto (宮本祐樹) S. Kuma (久間晋)
K. Kawaguchi (川口建太郎) A. Fukumi (福見敦)
T. Taniguchi (谷口敬)
Tokyo Institute of Technology I. Nakano (中野逸夫)
H. Kanamori (金森英人) N. Sasao (笹尾登)
M. Yoshimura (吉村太彦)
Motivation and Approach
• Searching for quantum coherence in isolated matrix:
demonstrate the ability to observe the phenomenon
for gaseous molecules, done or yet done
• Optical quantum coherence:
optical nutation, free induced decay (FID )
photon echo, and superradiance
• Linewidth of vibration-rotation transitions for gaseous mo
lecules (Doppler width ~100 MHz):
IR cw-lasers with narrow linewidth (<1 MHz)
Coherent transient effects
• Relaxation time: T1≳T2 (homo T2' and inhomo T2*)
• Absorption and coherent emission <T2
transient nutation, optical FID, photon echo
superradiance for population inverted levels
• Pulsed lasers or cw-lasers with either Stark (molecular)
switching or frequency switching
• Previous studies mainly with frequency-fixed IR lasers
• Recent development on the tunable cw-OPO laser provi
des us a new tool for the observation
Stark switching
• R. G. Brewer et al. (IBM, 1970s)
Stark pulsed field shift suddenly the absorption re
sonance from velocity group v to velocity group v'
Observations in 1970s
• With cw-CO2 laser (~6 W/cm2) in the 10μm region
13CH3FNH2D
optical nutation FIDphoton echo
R. G. Brewer et al., PRL&PRA (1971-1979)
13CH3F
13CH3F
“superradiance”
Present experiment
• CH3F 4 vibrational band @3m
weaker (~1/2) than 3 vibrational band @10m
• Observation first with the OPO laser in Okayama
~14 mW, <100 kHz, ~ 5 mm
w/o focusing ~ 0.14 W/cm2 « 6 W/cm2
no observation
Nutation and FID for pP3(4): J, K = 3, 2 4, 3
observed with focusing
CH3F inletVacuum
OPO IR laser
Stark cell
M
Lens 25 cm
CO2 laser, D = 2.7 mm, 6.3 W/cm2
OPO laser, D ~ 0.5 mm, 6 W/cm2
FID observed
With focusingDC Amp0-450 MHz
DetectorVIGO PVI-5<15 ns
PolarizationM=±1
Limit 2.5 W/cm2
CH3F inletVacuum
OPO IR laser
Stark cell
M
Lens 25 cm
Lens 5 cm
CO2 laser, D = 2.7 mm, 6.3 W/cm2
OPO laser, D ~ 0.7 mm, 3 W/cm2
FID Stronger!
With collimationDC Amp0-450 MHz
DetectorVIGO PVI-5<15 ns
PolarizationM=±1
Limit 2.5 W/cm2
0 mTorr1 mTorr1.5 mTorr2.5 mTorr3.0 mTorr4.0 mTorr6.0 mTorr11 mTorr15 mTorr19 mTorr24 mTorr32 mTorr37 mTorrPressure dependence
Average: 2000 times
±30 V/cm±15 V/cm0-30 V/cmStark field dependence
Stark splitting of transition
Δ M=+1
-3.5 -2.5 -1.5 -0.5 0.5 1.5 2.5 3.5
MHz
Intensity Δ M=-1
Δ M=0
ΔM= 0, 7 components
Relative intensity
ΔM= ±1, 14 components
43
-3
3
-3
2
-4
21
-2
-2
-1
-1
10
0
M
J, K = 3, 2
J, K = 4, 3
Optical Nutation and FID
22
241
)1(2
0/
0
0202
12
detector
0
)cos(
)(
)(
)cos()(
2
2
Td
tIAeI
ctJBeaI
III
EEEEEI
vtkzEEEE
M
MbM
dTtFID
TtNU
FIDNU
FIDNUavg
FIDNU
Hopf & Shea, PRA 7, 2105 (1973)
Simulation for FID and Nutation
T2 = 2.0 μs
= 2 MHz
Simulation: 4 mTorr
T2 = 0.73 μs
= 2 MHz
Simulation: 11 mTorr
Discussion
• T2·p = 7.96 s·mTorr ( from ref. )
p = 4 mTorr, T2 = 2.0 s
p = 11 mTorr, T2 = 0.73 s
• = 2 MHz, = ·E/h, I = 0E2/(2c)
= 0.086 D I = 3 W/cm⇒ 2
• Threshold of power density for FID & nutation
30 % of 3 W/cm2 1 W/cm2
( with linewidth <100 kHz )
Experiment with higher power OPO
• With the OPO laser of 200 mW (up to 600 mW)
Kanamori Lab in Tokyo Inst. Tech.
expanding the laser beam to ~1 inch
and then focusing with lens of f = 100 cm
• Observation for rR0(0): J, K = 1, 1 0, 0
nutation and FID: simple beat
photon echo: observed weakly
• Potential problem
high power density > detector limit 2.5 W/cm2
partially damaged?! ⇒ new detetor
CH3F inletVacuum
OPO IR laser200 mW
Stark cell
M
Lens 100 cm
CO2 laser, D = 2.7 mm, 6.3 W/cm2
OPO laser, D ~ 1 mm, 20 W/cm2
Compared with 5cm/25cm lens collimation
D ~ 2 mm, 5 W/cm2
Photo echo observed
Expanding & focusing
AC Amp-150 MHz
DetectorVIGO PVI-5<15 ns
PolarizationM=±1
Limit 2.5 W/cm2
Nutation and FID for rR0(0)0 0.1 0.2 0.3 0.4 0.5 0.6us
Stark field 100 V/ cm4 mTorr7.5 mTorr15 mTorr28 mTorr
FID beat vs. Stark field
0.0 0.2 0.4 0.6 0.8
- 0.6- 0.4- 0.20.00.20.40.6
← absorbance
signal(7.5mTorr) Stark voltage 20V
time(sec)
0
10
20
30 Stark vo
ltage(V
)
0.0 0.2 0.4 0.6 0.8
- 0.6- 0.4- 0.20.00.20.40.6
Stark voltage 50V
0.0 0.2 0.4 0.6 0.8
- 0.6- 0.4- 0.20.00.20.40.6
Stark voltage 100V
0 0.5 1 1.5 2 us
Stark Field
5 mT, 100 V/ cm
10 mT, 100 V/ cm20 mT, 100 V/ cm
Observation of photon echo for rR0(0)
0 50 100 150 200 250 300
0.00
0.01
0.02
0.03
0.04
frequency(MHz)
ampl
itude
0 50 100 150 200 250 300
0.0
0.1
0.2
Fourier transform for FID beat signal
Fourier transform for Photon Echo beat signal
am
plit
ud
e
Echo timing v.s. interval between two pulses
0.0 0.5 1.0 1.5 2.0
- 0.2
- 0.1
0.0
0.1
0.2
s
D
← a
bsor
ptio
n
time(sec)
signal(4mTorr, 100000 averages) Stark pulse(
s=240nsec
ON : 50V OFF :0V)~ 0
20
40
60
Stark voltage(V)
0.0 0.5 1.0 1.5 2.0
- 0.2
- 0.1
0.0
0.1
0.2
s=420nsec
0.0 0.5 1.0 1.5 2.0
- 0.2
- 0.1
0.0
0.1
0.2
s=600nsec
0
20
40
60
0
20
40
60
0.2 0.3 0.4 0.5 0.6
0.2
0.3
0.4
0.5
0.6
D(
sec)
s(sec)
dependence of D for
s
expected line
Photon echo with different Stark field0 0. 5 1 1. 5 2us
Stark fi el d10 mT, second pul se onl y10 mT, 50 V/ cm10 mT, 100 V/ cm
Summary & Future work
• We have observed optical nutation, FID, and photon echo for th
e 4 band of CH3F by cw-OPO lasers with Stark switching.
• With lens expanding, focusing, and collimating, a power density
larger than 3 W/cm2 has been reached for the 14 mW cw-OPO la
ser, and ~20 W/cm2 for the 200 mW cw-OPO laser.
• The next step would be to observe superradiance with the high p
ower cw-OPO laser for gaseous molecules.
• Frequency switching is another approach since Stark switching
may not be applicable to the isolated matrix, .