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, .